<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:c12445c2-ffe7-4d2b-ac30-4240a9beea59,g:c7b8e92d-feac-42c5-9045-77fb361ed62c-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="brlt-20210930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended" id="i16019d9aad8e4a9cb375e393ad5c7e29_CONDENSEDCONSOLIDATEDBALANCESHEETS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:to="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1d1eae69-257f-434b-8fd2-623479763af7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1d1eae69-257f-434b-8fd2-623479763af7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_dec894cb-21a1-4842-8265-4cde15c3f6ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:to="loc_us-gaap_RestrictedCashCurrent_dec894cb-21a1-4842-8265-4cde15c3f6ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_8590952b-a9ec-4ef2-9471-b79634d82e69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:to="loc_us-gaap_InventoryNet_8590952b-a9ec-4ef2-9471-b79634d82e69" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_9ff0646e-a475-4045-b7d4-e0f948852f4b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_9ff0646e-a475-4045-b7d4-e0f948852f4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_c8e678b8-4e5f-4e86-a5b9-bd07f98bccd9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9bdc57db-9d41-4c91-a10f-c63d1ef8a96c" xlink:to="loc_us-gaap_AssetsCurrent_c8e678b8-4e5f-4e86-a5b9-bd07f98bccd9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_60d2bc6c-3e00-48d1-9310-ee795b884ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_60d2bc6c-3e00-48d1-9310-ee795b884ea3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_93953b73-4226-459e-9300-d2757701a4be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_93953b73-4226-459e-9300-d2757701a4be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_e27d4ac1-e7ce-4844-ab7a-56cb09674302" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_e27d4ac1-e7ce-4844-ab7a-56cb09674302" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_70bc9516-0569-4935-ab0d-a8ba2be00df1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_0546bad0-3433-4516-960d-edaa2a01ac55" xlink:to="loc_us-gaap_Assets_70bc9516-0569-4935-ab0d-a8ba2be00df1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_5810f422-7124-4597-998f-6fea990f8b80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:to="loc_us-gaap_AccountsPayableCurrent_5810f422-7124-4597-998f-6fea990f8b80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_9398b911-8ee2-4580-aa7f-9b1701691180" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_9398b911-8ee2-4580-aa7f-9b1701691180" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_b9e1edef-d629-4d4d-b8cf-734388c21768" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_b9e1edef-d629-4d4d-b8cf-734388c21768" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_457d2d3f-f186-4977-bcc0-33f6544c04c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:to="loc_us-gaap_LongTermDebtCurrent_457d2d3f-f186-4977-bcc0-33f6544c04c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_922317f6-3cb6-4379-8869-662ae17a8021" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_b263bdb9-97e8-4e71-8669-1b50e2b549d8" xlink:to="loc_us-gaap_LiabilitiesCurrent_922317f6-3cb6-4379-8869-662ae17a8021" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_ba3c1267-2db8-4b6f-9bad-824de2fdc760" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_ba3c1267-2db8-4b6f-9bad-824de2fdc760" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_5af1101f-3815-4cc4-93e5-b29cabfdab93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_5af1101f-3815-4cc4-93e5-b29cabfdab93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRentCreditNoncurrent_ba6cf711-7cf6-4abf-a83a-59b6394776b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredRentCreditNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_DeferredRentCreditNoncurrent_ba6cf711-7cf6-4abf-a83a-59b6394776b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_WarrantLiability_675c8d07-dbe2-4d9b-9bc3-3d66acbcb183" xlink:href="brlt-20210930.xsd#brlt_WarrantLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_brlt_WarrantLiability_675c8d07-dbe2-4d9b-9bc3-3d66acbcb183" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_275b93e0-e085-4883-b3c5-c95411aad5b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccruedIncomeTaxesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_275b93e0-e085-4883-b3c5-c95411aad5b8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_1d762133-1b55-4a63-ba65-d75fbee8da20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_1d762133-1b55-4a63-ba65-d75fbee8da20" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_7ae0c745-b95f-4f35-a3fc-da48705b66cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_65e7ee11-7990-478d-b1d4-2843e4a2b239" xlink:to="loc_us-gaap_Liabilities_7ae0c745-b95f-4f35-a3fc-da48705b66cf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_86b2d22f-ffc2-4f38-aa96-c03004e1a2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_CommitmentsAndContingencies_86b2d22f-ffc2-4f38-aa96-c03004e1a2ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_b3cef8b2-242d-4a61-af71-cb8b0c49ce7b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_b3cef8b2-242d-4a61-af71-cb8b0c49ce7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquityAbstract_68814eaa-e2d7-417f-a30d-7e21626d45f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_MembersEquityAbstract_68814eaa-e2d7-417f-a30d-7e21626d45f1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_7ccfaa71-86c7-4bc1-840d-e3b12b0346ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_68814eaa-e2d7-417f-a30d-7e21626d45f1" xlink:to="loc_us-gaap_MembersEquity_7ccfaa71-86c7-4bc1-840d-e3b12b0346ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_cb6688a2-d9ce-40d4-b2ec-ef65cd646f31" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_PreferredStockValue_cb6688a2-d9ce-40d4-b2ec-ef65cd646f31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_d0412af1-fa1a-4f38-8998-df755695a2c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_CommonStockValue_d0412af1-fa1a-4f38-8998-df755695a2c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_902b61f9-a244-4a57-a903-233b1c90057b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_AdditionalPaidInCapital_902b61f9-a244-4a57-a903-233b1c90057b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_2fd63920-3199-4a4f-a311-e76671c62522" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_2fd63920-3199-4a4f-a311-e76671c62522" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_88b7c041-4bc2-475e-b4af-7a8bff70cbf6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_StockholdersEquity_88b7c041-4bc2-475e-b4af-7a8bff70cbf6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_bb942965-c069-410e-a5b4-ae6925ea5f3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_MinorityInterest_bb942965-c069-410e-a5b4-ae6925ea5f3b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7ca0c202-eeb3-4193-8e23-697d99ab4709" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7ca0c202-eeb3-4193-8e23-697d99ab4709" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityIncludingPortionAttributableToNoncontrollingInterestAndTemporaryEquity_8c4ad020-2218-4612-8d39-ae9811daec1a" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityIncludingPortionAttributableToNoncontrollingInterestAndTemporaryEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_5a3f08af-92da-4db3-9480-bb356bc11714" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityIncludingPortionAttributableToNoncontrollingInterestAndTemporaryEquity_8c4ad020-2218-4612-8d39-ae9811daec1a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_e71c62dc-ac17-40ce-a274-e193ba7a8c85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_e71c62dc-ac17-40ce-a274-e193ba7a8c85" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_85d47f99-cdb4-4b16-9206-2cce61706279" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_af63b638-3552-4962-a2f0-b44c961b1b98" xlink:to="loc_us-gaap_StatementTable_85d47f99-cdb4-4b16-9206-2cce61706279" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_b63376b4-9241-46e9-ab83-fe142a7434d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_85d47f99-cdb4-4b16-9206-2cce61706279" xlink:to="loc_us-gaap_StatementClassOfStockAxis_b63376b4-9241-46e9-ab83-fe142a7434d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_b63376b4-9241-46e9-ab83-fe142a7434d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b63376b4-9241-46e9-ab83-fe142a7434d4" xlink:to="loc_us-gaap_ClassOfStockDomain_b63376b4-9241-46e9-ab83-fe142a7434d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b63376b4-9241-46e9-ab83-fe142a7434d4" xlink:to="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFUnitsMember_a172b809-cdd7-4086-9e12-7a064afc2064" xlink:href="brlt-20210930.xsd#brlt_ClassFUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_brlt_ClassFUnitsMember_a172b809-cdd7-4086-9e12-7a064afc2064" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassMUnitsMember_d708e2ba-facf-4e8b-9139-36e6f03881ab" xlink:href="brlt-20210930.xsd#brlt_ClassMUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_brlt_ClassMUnitsMember_d708e2ba-facf-4e8b-9139-36e6f03881ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_877f9151-1e37-4883-a5ab-c72ff0bb70f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_us-gaap_CommonClassAMember_877f9151-1e37-4883-a5ab-c72ff0bb70f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_dddcea69-1f8c-4c6c-9a01-b452eed22b14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_us-gaap_CommonClassBMember_dddcea69-1f8c-4c6c-9a01-b452eed22b14" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_87ac79d3-5d2e-49c0-a906-7ed1b9137f85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_us-gaap_CommonClassCMember_87ac79d3-5d2e-49c0-a906-7ed1b9137f85" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonClassDMember_907972a8-744b-4a53-a514-62f95db9f17c" xlink:href="brlt-20210930.xsd#brlt_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fffb8272-22e8-447c-958a-967426cd9917" xlink:to="loc_brlt_CommonClassDMember_907972a8-744b-4a53-a514-62f95db9f17c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="brlt-20210930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended" id="if508463008134e129a2660f47c6ae5ba_CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_5f83fbb2-017a-4ce5-842c-fc76630092d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_5f83fbb2-017a-4ce5-842c-fc76630092d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_d81acd68-1619-436f-8b0b-c2319ec3863f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_d81acd68-1619-436f-8b0b-c2319ec3863f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_8b9c6ec3-1beb-42b4-9444-5f66042656a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_8b9c6ec3-1beb-42b4-9444-5f66042656a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitAuthorized_1e7c5e66-a67e-462e-9e27-df501e49d968" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonUnitAuthorized_1e7c5e66-a67e-462e-9e27-df501e49d968" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitIssued_932fcc6f-531e-4f1e-b619-73130764db55" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonUnitIssued_932fcc6f-531e-4f1e-b619-73130764db55" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_0fac0716-ccb6-4a03-8197-3a91362b7222" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonUnitOutstanding_0fac0716-ccb6-4a03-8197-3a91362b7222" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_9603c6a4-7b65-457c-aeb6-2c0bde523c8e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_9603c6a4-7b65-457c-aeb6-2c0bde523c8e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_29fc0a8e-c9c6-4e21-a181-bab6d0b2af34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_29fc0a8e-c9c6-4e21-a181-bab6d0b2af34" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_aae12178-6387-468d-a9e2-424e8f57ce21" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_PreferredStockSharesIssued_aae12178-6387-468d-a9e2-424e8f57ce21" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_6b1d144a-479d-4d88-a7b9-67757d5121c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_6b1d144a-479d-4d88-a7b9-67757d5121c0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_dadb8013-8f91-4b6e-ade2-998ded88c489" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_dadb8013-8f91-4b6e-ade2-998ded88c489" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_411357af-414f-4b36-875f-a141608359a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_411357af-414f-4b36-875f-a141608359a2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_13aa3783-ba24-4674-84f4-e0b7e42a7319" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonStockSharesIssued_13aa3783-ba24-4674-84f4-e0b7e42a7319" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f93b2629-adfe-41ab-8e9e-6e4845ecb499" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f93b2629-adfe-41ab-8e9e-6e4845ecb499" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_57369421-fec0-4708-80c2-5140355e7486" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_705be223-289a-4dba-a977-a55b1672ba2a" xlink:to="loc_us-gaap_StatementTable_57369421-fec0-4708-80c2-5140355e7486" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_74a57483-b7c3-4393-82db-451bd8716116" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_57369421-fec0-4708-80c2-5140355e7486" xlink:to="loc_us-gaap_StatementClassOfStockAxis_74a57483-b7c3-4393-82db-451bd8716116" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_74a57483-b7c3-4393-82db-451bd8716116_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_74a57483-b7c3-4393-82db-451bd8716116" xlink:to="loc_us-gaap_ClassOfStockDomain_74a57483-b7c3-4393-82db-451bd8716116_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_74a57483-b7c3-4393-82db-451bd8716116" xlink:to="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFUnitsMember_a50a35a8-cc36-4e7b-aa02-3e9aec877b42" xlink:href="brlt-20210930.xsd#brlt_ClassFUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_brlt_ClassFUnitsMember_a50a35a8-cc36-4e7b-aa02-3e9aec877b42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassMUnitsMember_805aa832-242e-4def-ba2d-e783ba0e94db" xlink:href="brlt-20210930.xsd#brlt_ClassMUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_brlt_ClassMUnitsMember_805aa832-242e-4def-ba2d-e783ba0e94db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_e8c8e3f3-ef58-4a63-bcad-56bdaedeb758" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_us-gaap_CommonClassAMember_e8c8e3f3-ef58-4a63-bcad-56bdaedeb758" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_64968817-85ed-4f0c-9c7a-5790cea9a7ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_us-gaap_CommonClassBMember_64968817-85ed-4f0c-9c7a-5790cea9a7ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_56103cfc-3141-40bf-8413-b9eb8adb0344" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_us-gaap_CommonClassCMember_56103cfc-3141-40bf-8413-b9eb8adb0344" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonClassDMember_e0260c72-36ed-4a01-836e-b90643041442" xlink:href="brlt-20210930.xsd#brlt_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1e51da98-f08a-4e33-a6e1-55633a1097e5" xlink:to="loc_brlt_CommonClassDMember_e0260c72-36ed-4a01-836e-b90643041442" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYDEFICIT" xlink:type="simple" xlink:href="brlt-20210930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYDEFICIT"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYDEFICIT" xlink:type="extended" id="i0c4a8f5c9577494fac80b8ade4819114_CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYDEFICIT">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_a5d7fb63-7b31-4f30-acb9-44fa7a5d1c4a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a5d7fb63-7b31-4f30-acb9-44fa7a5d1c4a" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_e96216fe-7811-4ee2-83ae-a4c2df18b848" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_e96216fe-7811-4ee2-83ae-a4c2df18b848" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_3c282135-3544-4648-8e00-e59a7a34ef80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_3c282135-3544-4648-8e00-e59a7a34ef80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TemporaryEquityTaxDistributionsToMembers_0fc093a7-388a-4a23-89fb-52f24bc47a9b" xlink:href="brlt-20210930.xsd#brlt_TemporaryEquityTaxDistributionsToMembers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_brlt_TemporaryEquityTaxDistributionsToMembers_0fc093a7-388a-4a23-89fb-52f24bc47a9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityNetIncome_605195bb-036d-4b23-95b9-4083774913bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityNetIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_us-gaap_TemporaryEquityNetIncome_605195bb-036d-4b23-95b9-4083774913bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_b34b5d89-0156-46c4-ad88-6d85ac7c5898" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_b34b5d89-0156-46c4-ad88-6d85ac7c5898" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TemporaryEquityEliminationAsPartOfReorganizationShares_235a41ac-9b33-43b5-b67e-a9f5e59eaa91" xlink:href="brlt-20210930.xsd#brlt_TemporaryEquityEliminationAsPartOfReorganizationShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_brlt_TemporaryEquityEliminationAsPartOfReorganizationShares_235a41ac-9b33-43b5-b67e-a9f5e59eaa91" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_7e1ce4ad-b38a-4c2b-8095-71d66885444a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityEliminationAsPartofReorganization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_dcdb4c32-14c4-4a35-9c4a-6ba56e936097" xlink:to="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_7e1ce4ad-b38a-4c2b-8095-71d66885444a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_41df2231-c2c2-47d7-b2f9-916e32bb4dc0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_cf25e31d-e24c-48d0-bd04-06c6ee98d7ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a5d7fb63-7b31-4f30-acb9-44fa7a5d1c4a" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_155a2365-009f-4c40-861d-36fca0b38b1c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_CommonUnitOutstanding_155a2365-009f-4c40-861d-36fca0b38b1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_d354049f-9a07-4211-96dd-4adc860bb4d0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_MembersEquity_d354049f-9a07-4211-96dd-4adc860bb4d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers_f7116d97-1120-4a12-b85e-1b5f6a758b43" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers_f7116d97-1120-4a12-b85e-1b5f6a758b43" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares_e548f730-111a-4066-aa3e-ee4b90f4df85" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares_e548f730-111a-4066-aa3e-ee4b90f4df85" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation_2b819acc-e356-4df2-8649-22d8e5db1ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation_2b819acc-e356-4df2-8649-22d8e5db1ad6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_ecd4bd9a-5af8-491c-b27f-a219b0a1d074" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_ProfitLoss_ecd4bd9a-5af8-491c-b27f-a219b0a1d074" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestBeforeReorganizationAndInitialPublicOffering_7702bdb5-d806-4bda-9305-6aa930db47f1" xlink:href="brlt-20210930.xsd#brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestBeforeReorganizationAndInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestBeforeReorganizationAndInitialPublicOffering_7702bdb5-d806-4bda-9305-6aa930db47f1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment_a28667d8-9de2-4b00-b995-c018504e95f6" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment_a28667d8-9de2-4b00-b995-c018504e95f6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_b85df0f2-2e74-4bcd-97b4-3b187b4fe2ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_b85df0f2-2e74-4bcd-97b4-3b187b4fe2ab" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_65eb4607-d71f-4484-8e82-24c2be6b6dea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_65eb4607-d71f-4484-8e82-24c2be6b6dea" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_3ea3e9a9-81d0-44d0-83a8-bfbae62cb631" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_3ea3e9a9-81d0-44d0-83a8-bfbae62cb631" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_fa68eb09-22be-48f1-93e3-f50df61dea02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_fa68eb09-22be-48f1-93e3-f50df61dea02" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_AdjustmentsToAdditionalPaidInCapitalDeferredTaxAdjustment_339134e0-74d7-4c2f-9a4f-035a87e431d9" xlink:href="brlt-20210930.xsd#brlt_AdjustmentsToAdditionalPaidInCapitalDeferredTaxAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_AdjustmentsToAdditionalPaidInCapitalDeferredTaxAdjustment_339134e0-74d7-4c2f-9a4f-035a87e431d9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_98d033d4-d1f2-4d1c-ae5a-70d0166d55b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_98d033d4-d1f2-4d1c-ae5a-70d0166d55b8" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b8635edf-a15b-4edf-84e6-a8d5a98051ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b8635edf-a15b-4edf-84e6-a8d5a98051ce" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestAfterReorganizationAndInitialPublicOffering_ceff0ff8-d1e6-4d30-ad1a-cb4428825cd4" xlink:href="brlt-20210930.xsd#brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestAfterReorganizationAndInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_brlt_NetIncomeLossIncludingPortionAttributableToNoncontrollingInterestAfterReorganizationAndInitialPublicOffering_ceff0ff8-d1e6-4d30-ad1a-cb4428825cd4" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_3d71e4c6-79dd-4eca-9b26-708df22fa02f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_cb6237bc-eaa2-40ad-a0ce-fede49d2022d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_3c4b60dc-7a9a-4da7-898c-06925703e59f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_3c4b60dc-7a9a-4da7-898c-06925703e59f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_520c7c05-27a0-4816-8be1-6695257a51ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e433b72b-996f-40ae-a4fe-4dd214b4ea34" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_520c7c05-27a0-4816-8be1-6695257a51ab" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_522a42ca-e41b-4ec1-92a9-74cf644ca0c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_a5d7fb63-7b31-4f30-acb9-44fa7a5d1c4a" xlink:to="loc_us-gaap_StatementTable_522a42ca-e41b-4ec1-92a9-74cf644ca0c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_46cfd802-5397-45d0-85d9-87616c347457" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_522a42ca-e41b-4ec1-92a9-74cf644ca0c1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_46cfd802-5397-45d0-85d9-87616c347457" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_46cfd802-5397-45d0-85d9-87616c347457_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_46cfd802-5397-45d0-85d9-87616c347457" xlink:to="loc_us-gaap_ClassOfStockDomain_46cfd802-5397-45d0-85d9-87616c347457_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e16260c0-8a2e-428b-8daf-0ad10be1cd19" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_46cfd802-5397-45d0-85d9-87616c347457" xlink:to="loc_us-gaap_ClassOfStockDomain_e16260c0-8a2e-428b-8daf-0ad10be1cd19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_400af626-8326-4c7f-9586-a4e492c15354" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e16260c0-8a2e-428b-8daf-0ad10be1cd19" xlink:to="loc_us-gaap_CommonClassAMember_400af626-8326-4c7f-9586-a4e492c15354" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_1a874b13-4a61-4867-8836-c3a353cdf797" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e16260c0-8a2e-428b-8daf-0ad10be1cd19" xlink:to="loc_us-gaap_CommonClassBMember_1a874b13-4a61-4867-8836-c3a353cdf797" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_d72cb09f-584a-4843-8af7-19b4ce207d38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e16260c0-8a2e-428b-8daf-0ad10be1cd19" xlink:to="loc_us-gaap_CommonClassCMember_d72cb09f-584a-4843-8af7-19b4ce207d38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ea55eed5-0440-4528-a324-2f34e564516f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_522a42ca-e41b-4ec1-92a9-74cf644ca0c1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ea55eed5-0440-4528-a324-2f34e564516f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ea55eed5-0440-4528-a324-2f34e564516f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ea55eed5-0440-4528-a324-2f34e564516f" xlink:to="loc_us-gaap_EquityComponentDomain_ea55eed5-0440-4528-a324-2f34e564516f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ea55eed5-0440-4528-a324-2f34e564516f" xlink:to="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MemberUnitsMember_d17512a8-56c0-43f1-8da0-90d08f1c5e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MemberUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_MemberUnitsMember_d17512a8-56c0-43f1-8da0-90d08f1c5e9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_259c9db2-f309-4713-b7b6-cbde33f96e41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_CommonStockMember_259c9db2-f309-4713-b7b6-cbde33f96e41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_3cf26ab2-45c3-4531-9610-e22dc2e11522" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_3cf26ab2-45c3-4531-9610-e22dc2e11522" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_0f87068e-25cb-4bb4-b7d3-9714e9ad9916" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_RetainedEarningsMember_0f87068e-25cb-4bb4-b7d3-9714e9ad9916" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_0dde3c50-dedd-4e7e-9774-0e28d97efb17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_ParentMember_0dde3c50-dedd-4e7e-9774-0e28d97efb17" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_78446032-a5c8-49d5-a607-a892e020c303" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f34adb5d-fb5a-4c08-8854-f576e5b090fa" xlink:to="loc_us-gaap_NoncontrollingInterestMember_78446032-a5c8-49d5-a607-a892e020c303" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="simple" xlink:href="brlt-20210930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="extended" id="i7bf5dc77ab4f420e91c5fc383a86b43d_CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_bd62b90a-cc96-49de-9739-c7840283f036" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_bd62b90a-cc96-49de-9739-c7840283f036" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_430e4119-99cb-40b4-9fcf-26c51990c7d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_bd62b90a-cc96-49de-9739-c7840283f036" xlink:to="loc_us-gaap_ProfitLoss_430e4119-99cb-40b4-9fcf-26c51990c7d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_bd62b90a-cc96-49de-9739-c7840283f036" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_bc2cf04f-7d17-4a4a-968b-8a99880d39de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_Depreciation_bc2cf04f-7d17-4a4a-968b-8a99880d39de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_9f5eb222-f914-48d0-9bee-8f8ffef6eaee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_ShareBasedCompensation_9f5eb222-f914-48d0-9bee-8f8ffef6eaee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_c593b432-8d43-4a6d-9bbc-fa67462efaad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAdjustmentOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_c593b432-8d43-4a6d-9bbc-fa67462efaad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_9af308c0-402b-46f8-8126-dd4cf07c189d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_9af308c0-402b-46f8-8126-dd4cf07c189d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_f40b487c-9240-40a9-a509-9e1d78e88a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherOperatingActivitiesCashFlowStatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_f40b487c-9240-40a9-a509-9e1d78e88a1a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c458b0f3-7f65-46ee-8f08-9c50b8d3b96e" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_e9b3e87a-73ba-4856-b56c-f1a2f6f98970" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_e9b3e87a-73ba-4856-b56c-f1a2f6f98970" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_d8bd9072-2fd3-474d-a02b-bf4fd25de9e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_d8bd9072-2fd3-474d-a02b-bf4fd25de9e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_bec4b166-c7c5-4673-b28b-3aa31644b116" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_bec4b166-c7c5-4673-b28b-3aa31644b116" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_e743bc29-e293-4b95-9914-07e6546f7233" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_e743bc29-e293-4b95-9914-07e6546f7233" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_228913e0-d6ed-48a5-baee-926dfb2e4ea8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_228913e0-d6ed-48a5-baee-926dfb2e4ea8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredCharges_05eb6c74-c315-4488-ba1d-fe67f58695be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_7e0d8e7d-554d-4f4f-a73c-529eb0b64937" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredCharges_05eb6c74-c315-4488-ba1d-fe67f58695be" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7ddccb0b-2420-4ce3-98dd-ff3d9c9699a5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_bd62b90a-cc96-49de-9739-c7840283f036" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7ddccb0b-2420-4ce3-98dd-ff3d9c9699a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_bc5c47ca-a38b-486f-b2cb-6de93280b419" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_bc5c47ca-a38b-486f-b2cb-6de93280b419" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_10c01302-fc05-4a78-b87e-971273f1e097" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_bc5c47ca-a38b-486f-b2cb-6de93280b419" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_10c01302-fc05-4a78-b87e-971273f1e097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_bffe366d-775f-4576-9987-fc23d6155f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_bc5c47ca-a38b-486f-b2cb-6de93280b419" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_bffe366d-775f-4576-9987-fc23d6155f2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_c9d63779-b8f0-4601-9de9-ae5476b31e67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_c9d63779-b8f0-4601-9de9-ae5476b31e67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_cd6cd538-893c-4ba5-9b58-fdb0e7d9ad39" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_cd6cd538-893c-4ba5-9b58-fdb0e7d9ad39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_1c375bf1-a82e-4b04-8447-1580cf4e51c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_1c375bf1-a82e-4b04-8447-1580cf4e51c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDistributionsToAffiliates_207ee25d-b0c9-4dc8-a6e3-aec3f895b18c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDistributionsToAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_PaymentsOfDistributionsToAffiliates_207ee25d-b0c9-4dc8-a6e3-aec3f895b18c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_9950451a-3575-4083-9039-a5653e890acc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_9950451a-3575-4083-9039-a5653e890acc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_496b9796-4434-44f7-a471-db18e9f6a8c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_496b9796-4434-44f7-a471-db18e9f6a8c4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_e9811ed7-0895-44d7-8ee2-42896c52cdde" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_92ec05a6-1ad6-45b2-a2fd-41ffe40e10dd" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_e9811ed7-0895-44d7-8ee2-42896c52cdde" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_3204685d-ee01-4d6d-b8b6-cd60ffcc8e07" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_3204685d-ee01-4d6d-b8b6-cd60ffcc8e07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_46b29ebe-3146-4695-9b7b-26efed67d466" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_46b29ebe-3146-4695-9b7b-26efed67d466" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_b9e16ae2-b71d-4543-bcf0-3702d13bec58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_AdjustmentOfRedeemableConvertiblePreferredUnitsToRedemptionValue_2e251de0-7fcd-4ff6-93f6-37a1bd9cdb40" xlink:href="brlt-20210930.xsd#brlt_AdjustmentOfRedeemableConvertiblePreferredUnitsToRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_AdjustmentOfRedeemableConvertiblePreferredUnitsToRedemptionValue_2e251de0-7fcd-4ff6-93f6-37a1bd9cdb40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockAmountConverted1_e0281a92-b017-4196-8b49-01187f501eae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockAmountConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_us-gaap_ConversionOfStockAmountConverted1_e0281a92-b017-4196-8b49-01187f501eae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NetExerciseOfWarrants_a44d1da1-7d12-4407-b89d-a972b101736e" xlink:href="brlt-20210930.xsd#brlt_NetExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_NetExerciseOfWarrants_a44d1da1-7d12-4407-b89d-a972b101736e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_StockIssuanceCostsIncurredButNotYetPaid_d07a4172-1b88-4265-8536-3b830618a4c5" xlink:href="brlt-20210930.xsd#brlt_StockIssuanceCostsIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_StockIssuanceCostsIncurredButNotYetPaid_d07a4172-1b88-4265-8536-3b830618a4c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DeferredTaxAssetsAssociatedWithRedemptionOfUnits_9b819dbb-35ba-4774-9cf6-0c65d8e6c6bf" xlink:href="brlt-20210930.xsd#brlt_DeferredTaxAssetsAssociatedWithRedemptionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_DeferredTaxAssetsAssociatedWithRedemptionOfUnits_9b819dbb-35ba-4774-9cf6-0c65d8e6c6bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TaxReceivableAgreementObligationAssociatedWithRedemptionOfUnits_dbb2c02e-1604-453b-ad0c-3c9f8d6ac144" xlink:href="brlt-20210930.xsd#brlt_TaxReceivableAgreementObligationAssociatedWithRedemptionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_TaxReceivableAgreementObligationAssociatedWithRedemptionOfUnits_dbb2c02e-1604-453b-ad0c-3c9f8d6ac144" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CreditToAdditionalPaidInCapitalRelatedToRedemptionOfUnits_42cc6827-6db4-4cda-b7bb-26c7db0338fe" xlink:href="brlt-20210930.xsd#brlt_CreditToAdditionalPaidInCapitalRelatedToRedemptionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_CreditToAdditionalPaidInCapitalRelatedToRedemptionOfUnits_42cc6827-6db4-4cda-b7bb-26c7db0338fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtIssuanceCostsCapitalizedToPrincipalOfLongTermDebt_7452a3cb-d157-4736-8e9b-53698d078487" xlink:href="brlt-20210930.xsd#brlt_DebtIssuanceCostsCapitalizedToPrincipalOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_brlt_DebtIssuanceCostsCapitalizedToPrincipalOfLongTermDebt_7452a3cb-d157-4736-8e9b-53698d078487" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_06e30b76-fe6e-4ec6-8c40-303852900506" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9b9f3a71-5563-485c-b010-44c4e9481a41" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_06e30b76-fe6e-4ec6-8c40-303852900506" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowElementsAbstract_1c21b249-543e-4a91-9e4a-98e3fc747cf9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SupplementalCashFlowElementsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_SupplementalCashFlowElementsAbstract_1c21b249-543e-4a91-9e4a-98e3fc747cf9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_1e3732c9-f2d9-4460-ae25-e74befb4f891" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowElementsAbstract_1c21b249-543e-4a91-9e4a-98e3fc747cf9" xlink:to="loc_us-gaap_InterestPaidNet_1e3732c9-f2d9-4460-ae25-e74befb4f891" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6c5f8598-db43-40a7-8e2a-ead92f53e290" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0033de7a-b5c7-4731-a743-93b9d055e876" xlink:to="loc_us-gaap_StatementTable_6c5f8598-db43-40a7-8e2a-ead92f53e290" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6c5f8598-db43-40a7-8e2a-ead92f53e290" xlink:to="loc_us-gaap_StatementClassOfStockAxis_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e" xlink:to="loc_us-gaap_ClassOfStockDomain_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c792b9fd-e868-47a4-9246-eac73e8b1edc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_255b7ba1-baff-4f5d-84fc-d63ec09d0e6e" xlink:to="loc_us-gaap_ClassOfStockDomain_c792b9fd-e868-47a4-9246-eac73e8b1edc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFUnitsAndClassMUnitsMember_566594a5-2c25-4573-9cb7-6781109fc462" xlink:href="brlt-20210930.xsd#brlt_ClassFUnitsAndClassMUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c792b9fd-e868-47a4-9246-eac73e8b1edc" xlink:to="loc_brlt_ClassFUnitsAndClassMUnitsMember_566594a5-2c25-4573-9cb7-6781109fc462" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassPUnitsMember_73a7fc21-96c6-4cf5-85cd-e62516d545cc" xlink:href="brlt-20210930.xsd#brlt_ClassPUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c792b9fd-e868-47a4-9246-eac73e8b1edc" xlink:to="loc_brlt_ClassPUnitsMember_73a7fc21-96c6-4cf5-85cd-e62516d545cc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/BusinessandOrganizationDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#BusinessandOrganizationDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/BusinessandOrganizationDetails" xlink:type="extended" id="iaa475cdd081e4e38a69d5ce7c16b1025_BusinessandOrganizationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_b64b3a20-d27b-4ac1-b19a-e38944958ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_NumberOfOperatingSegments_b64b3a20-d27b-4ac1-b19a-e38944958ed3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_9ebfd8a8-d8eb-4e8b-a4de-94dee3168ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_NumberOfReportableSegments_9ebfd8a8-d8eb-4e8b-a4de-94dee3168ca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_22635ab5-d8e0-47bb-95ce-be99756498a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_22635ab5-d8e0-47bb-95ce-be99756498a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_91004e7a-5c19-4446-b25c-0b2444684c62" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_91004e7a-5c19-4446-b25c-0b2444684c62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_d73f211b-7ecc-482b-9559-bf7bc5bee6b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_d73f211b-7ecc-482b-9559-bf7bc5bee6b9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_42e8c520-78c4-4b81-ab47-b6fc10f8977e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_42e8c520-78c4-4b81-ab47-b6fc10f8977e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_889b35f6-b7a9-4382-be51-c45c77eb740b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_889b35f6-b7a9-4382-be51-c45c77eb740b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NoncontrollingInterestNumberOfSharesPurchased_32d62707-8435-4930-b65b-671f8b488b72" xlink:href="brlt-20210930.xsd#brlt_NoncontrollingInterestNumberOfSharesPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_NoncontrollingInterestNumberOfSharesPurchased_32d62707-8435-4930-b65b-671f8b488b72" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_SaleOfStockPricePerShareNetOfUnderwritingDiscount_10304858-95cb-4ad6-9d25-b54ae697d476" xlink:href="brlt-20210930.xsd#brlt_SaleOfStockPricePerShareNetOfUnderwritingDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_SaleOfStockPricePerShareNetOfUnderwritingDiscount_10304858-95cb-4ad6-9d25-b54ae697d476" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest_66e9ab5b-b843-42a4-a4d7-35126d65cd58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest_66e9ab5b-b843-42a4-a4d7-35126d65cd58" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesIssued1_d9016fd0-f7e2-4ee0-86b1-7fc9fd28fd5a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_ConversionOfStockSharesIssued1_d9016fd0-f7e2-4ee0-86b1-7fc9fd28fd5a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ConversionOfStockAwardsConversionRatio_68b0b09a-9540-4b45-a7ed-c6132324b771" xlink:href="brlt-20210930.xsd#brlt_ConversionOfStockAwardsConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_ConversionOfStockAwardsConversionRatio_68b0b09a-9540-4b45-a7ed-c6132324b771" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_fbf1c12e-cd08-4d6e-8521-bf55fb84d0e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_fbf1c12e-cd08-4d6e-8521-bf55fb84d0e8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_ec7625f8-cfd2-4caa-b52c-00b3b3e12a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_ec7625f8-cfd2-4caa-b52c-00b3b3e12a6f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent_3bc3049f-0264-49b2-a480-85936fd27821" xlink:href="brlt-20210930.xsd#brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent_3bc3049f-0264-49b2-a480-85936fd27821" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_9ef47068-8173-4541-97d9-e057122e4c23" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestDecreaseFromRedemptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_9ef47068-8173-4541-97d9-e057122e4c23" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonStockSharesCancelled_f74d7ad5-4230-4a7d-b3cb-80d004641e10" xlink:href="brlt-20210930.xsd#brlt_CommonStockSharesCancelled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_CommonStockSharesCancelled_f74d7ad5-4230-4a7d-b3cb-80d004641e10" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassOfWarrantOrRightCarryingValue_1c0d8b4b-17be-4b02-8888-bd4387c8a261" xlink:href="brlt-20210930.xsd#brlt_ClassOfWarrantOrRightCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_brlt_ClassOfWarrantOrRightCarryingValue_1c0d8b4b-17be-4b02-8888-bd4387c8a261" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_2045c0b0-17a1-45dd-8b74-ad0cfa77a26b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_2045c0b0-17a1-45dd-8b74-ad0cfa77a26b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_b1b834e3-2307-4816-9c37-d2a0735ee12c" xlink:to="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f1ae02dc-a196-4170-bd58-f9dd02f34f91" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f1ae02dc-a196-4170-bd58-f9dd02f34f91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f1ae02dc-a196-4170-bd58-f9dd02f34f91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f1ae02dc-a196-4170-bd58-f9dd02f34f91" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f1ae02dc-a196-4170-bd58-f9dd02f34f91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_dbf3699c-072b-439e-bd0f-337def483970" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f1ae02dc-a196-4170-bd58-f9dd02f34f91" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_dbf3699c-072b-439e-bd0f-337def483970" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_b2ef0218-8214-4994-ba72-566857c97139" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_dbf3699c-072b-439e-bd0f-337def483970" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_b2ef0218-8214-4994-ba72-566857c97139" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_701322c4-a4f4-485d-b499-3b6935069625" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_701322c4-a4f4-485d-b499-3b6935069625" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_701322c4-a4f4-485d-b499-3b6935069625_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_701322c4-a4f4-485d-b499-3b6935069625" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_701322c4-a4f4-485d-b499-3b6935069625_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c25c7003-e9ec-4ced-bc39-93640c2ebee6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_701322c4-a4f4-485d-b499-3b6935069625" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c25c7003-e9ec-4ced-bc39-93640c2ebee6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_c6e1f8dd-0131-4341-920d-bd93fa6de97d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_c25c7003-e9ec-4ced-bc39-93640c2ebee6" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_c6e1f8dd-0131-4341-920d-bd93fa6de97d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_152e4e7e-d722-47cb-8b6e-f198749705dc" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_srt_StatementGeographicalAxis_152e4e7e-d722-47cb-8b6e-f198749705dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_152e4e7e-d722-47cb-8b6e-f198749705dc_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_152e4e7e-d722-47cb-8b6e-f198749705dc" xlink:to="loc_srt_SegmentGeographicalDomain_152e4e7e-d722-47cb-8b6e-f198749705dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_6ac245aa-d045-4eee-8524-851c3af8704e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_152e4e7e-d722-47cb-8b6e-f198749705dc" xlink:to="loc_srt_SegmentGeographicalDomain_6ac245aa-d045-4eee-8524-851c3af8704e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_623774a8-4466-4b57-81f0-9a6fb137ebcb" xlink:href="https://xbrl.sec.gov/country/2021/country-2021.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_6ac245aa-d045-4eee-8524-851c3af8704e" xlink:to="loc_country_US_623774a8-4466-4b57-81f0-9a6fb137ebcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9a877440-4661-414b-9837-8ecb3530d8c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_51ca13eb-d827-42f1-99a0-cdb24c6f2c4d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9a877440-4661-414b-9837-8ecb3530d8c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_f42c182f-976b-4c76-85c3-b598ff9c0daa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9a877440-4661-414b-9837-8ecb3530d8c9" xlink:to="loc_us-gaap_IPOMember_f42c182f-976b-4c76-85c3-b598ff9c0daa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_8a0688d7-36a5-4004-b31d-c53284371692" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9a877440-4661-414b-9837-8ecb3530d8c9" xlink:to="loc_us-gaap_OverAllotmentOptionMember_8a0688d7-36a5-4004-b31d-c53284371692" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_32f98a2f-bd9b-4326-96f0-4086fee7eb71" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_srt_CounterpartyNameAxis_32f98a2f-bd9b-4326-96f0-4086fee7eb71" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_32f98a2f-bd9b-4326-96f0-4086fee7eb71_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_32f98a2f-bd9b-4326-96f0-4086fee7eb71" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_32f98a2f-bd9b-4326-96f0-4086fee7eb71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_421555fc-c1e0-478c-bc41-d583767744ac" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_32f98a2f-bd9b-4326-96f0-4086fee7eb71" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_421555fc-c1e0-478c-bc41-d583767744ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_e5cb405e-a46f-4abc-a1e6-25e0335a7bf2" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_421555fc-c1e0-478c-bc41-d583767744ac" xlink:to="loc_brlt_BrilliantEarthLLCMember_e5cb405e-a46f-4abc-a1e6-25e0335a7bf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContinuingEquityOwnersMember_b346e7ca-7c52-4f54-ac06-cd45a90dcdda" xlink:href="brlt-20210930.xsd#brlt_ContinuingEquityOwnersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_421555fc-c1e0-478c-bc41-d583767744ac" xlink:to="loc_brlt_ContinuingEquityOwnersMember_b346e7ca-7c52-4f54-ac06-cd45a90dcdda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_dccfa9b3-a862-49bf-b722-76aea39b5f8c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_srt_OwnershipAxis_dccfa9b3-a862-49bf-b722-76aea39b5f8c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_dccfa9b3-a862-49bf-b722-76aea39b5f8c_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_dccfa9b3-a862-49bf-b722-76aea39b5f8c" xlink:to="loc_srt_OwnershipDomain_dccfa9b3-a862-49bf-b722-76aea39b5f8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_84e9de60-c832-4c7b-91af-d2341b61f6b6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_dccfa9b3-a862-49bf-b722-76aea39b5f8c" xlink:to="loc_srt_OwnershipDomain_84e9de60-c832-4c7b-91af-d2341b61f6b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_bb2bffd9-4123-4feb-ab51-a97e81691699" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_84e9de60-c832-4c7b-91af-d2341b61f6b6" xlink:to="loc_brlt_BrilliantEarthLLCMember_bb2bffd9-4123-4feb-ab51-a97e81691699" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_57ac0192-a4d2-47ac-8c28-c27cba49841f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_57ac0192-a4d2-47ac-8c28-c27cba49841f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_57ac0192-a4d2-47ac-8c28-c27cba49841f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_57ac0192-a4d2-47ac-8c28-c27cba49841f" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_57ac0192-a4d2-47ac-8c28-c27cba49841f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_57ac0192-a4d2-47ac-8c28-c27cba49841f" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFPAndMUnitsConvertedIntoCommonLLCUnitsMember_46ebd5b0-1073-425d-bf78-0a39a1ad2c6e" xlink:href="brlt-20210930.xsd#brlt_ClassFPAndMUnitsConvertedIntoCommonLLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:to="loc_brlt_ClassFPAndMUnitsConvertedIntoCommonLLCUnitsMember_46ebd5b0-1073-425d-bf78-0a39a1ad2c6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFUnitsConvertedIntoCommonLLCUnitsMember_d87d9d19-f72a-4f8d-abf5-26471c1be688" xlink:href="brlt-20210930.xsd#brlt_ClassFUnitsConvertedIntoCommonLLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:to="loc_brlt_ClassFUnitsConvertedIntoCommonLLCUnitsMember_d87d9d19-f72a-4f8d-abf5-26471c1be688" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassPUnitsConvertedIntoCommonLLCUnitsMember_492a4d11-c86b-4c0b-8856-79f75fddafa1" xlink:href="brlt-20210930.xsd#brlt_ClassPUnitsConvertedIntoCommonLLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:to="loc_brlt_ClassPUnitsConvertedIntoCommonLLCUnitsMember_492a4d11-c86b-4c0b-8856-79f75fddafa1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassMUnitsConvertedIntoCommonLLCUnitsMember_b08fc7dc-b2be-4099-acee-1a58db296989" xlink:href="brlt-20210930.xsd#brlt_ClassMUnitsConvertedIntoCommonLLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:to="loc_brlt_ClassMUnitsConvertedIntoCommonLLCUnitsMember_b08fc7dc-b2be-4099-acee-1a58db296989" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember_db97c370-632f-4290-878c-4ddce2005e35" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_21c652c4-bf52-45bd-8452-a1e15bbe351b" xlink:to="loc_brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember_db97c370-632f-4290-878c-4ddce2005e35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_19059990-9aa4-41b1-905a-ca3af396ca71" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_19059990-9aa4-41b1-905a-ca3af396ca71" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_19059990-9aa4-41b1-905a-ca3af396ca71_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_19059990-9aa4-41b1-905a-ca3af396ca71" xlink:to="loc_us-gaap_ClassOfStockDomain_19059990-9aa4-41b1-905a-ca3af396ca71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_19059990-9aa4-41b1-905a-ca3af396ca71" xlink:to="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_143ac1ba-042b-4238-acd5-6048eb137cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:to="loc_us-gaap_CommonClassAMember_143ac1ba-042b-4238-acd5-6048eb137cb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_c73ffcaf-fd1b-41e9-8108-17a54895b23a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:to="loc_us-gaap_CommonClassBMember_c73ffcaf-fd1b-41e9-8108-17a54895b23a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_26581dc7-8317-402e-91b0-6415ed3842a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:to="loc_us-gaap_CommonClassCMember_26581dc7-8317-402e-91b0-6415ed3842a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassBAndClassCCommonStockMember_335777fc-af44-49ea-8240-97fdfa371573" xlink:href="brlt-20210930.xsd#brlt_ClassBAndClassCCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:to="loc_brlt_ClassBAndClassCCommonStockMember_335777fc-af44-49ea-8240-97fdfa371573" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MemberUnitsMember_d830d3a6-300e-45da-b003-163d177b044d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MemberUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c637309b-b820-4572-940b-a694f13a6702" xlink:to="loc_us-gaap_MemberUnitsMember_d830d3a6-300e-45da-b003-163d177b044d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_008cd6eb-f925-46aa-b7e3-b02612b8e676" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_a4762183-f42f-4c95-89fa-7348c47945f8" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_008cd6eb-f925-46aa-b7e3-b02612b8e676" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_008cd6eb-f925-46aa-b7e3-b02612b8e676_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_008cd6eb-f925-46aa-b7e3-b02612b8e676" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_008cd6eb-f925-46aa-b7e3-b02612b8e676_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_67a159c2-612a-402a-a73c-aef7c340c109" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_008cd6eb-f925-46aa-b7e3-b02612b8e676" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_67a159c2-612a-402a-a73c-aef7c340c109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassPWarrantsMember_86c0ed68-d283-425c-9000-56325824f150" xlink:href="brlt-20210930.xsd#brlt_ClassPWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_67a159c2-612a-402a-a73c-aef7c340c109" xlink:to="loc_brlt_ClassPWarrantsMember_86c0ed68-d283-425c-9000-56325824f150" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended" id="if9222aac926745cc901c028a70aa50d6_SummaryofSignificantAccountingPoliciesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_53e3fc54-0a2b-42e1-a26f-1788cf9ea6db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_53e3fc54-0a2b-42e1-a26f-1788cf9ea6db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityFairValue_7b9e427b-e732-431f-8c94-174021a98c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityFairValue_7b9e427b-e732-431f-8c94-174021a98c7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_WarrantLiabilityFairValueDisclosure_cc809e5a-5637-4284-9403-370e948727dd" xlink:href="brlt-20210930.xsd#brlt_WarrantLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_brlt_WarrantLiabilityFairValueDisclosure_cc809e5a-5637-4284-9403-370e948727dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContractWithCustomerReturnPeriod_502488e4-670e-4598-848e-789fe0f29a1a" xlink:href="brlt-20210930.xsd#brlt_ContractWithCustomerReturnPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_brlt_ContractWithCustomerReturnPeriod_502488e4-670e-4598-848e-789fe0f29a1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContractWithCustomerResizingPeriod_01d5aefa-d72b-4e82-aebe-6fbb1f5ccdcc" xlink:href="brlt-20210930.xsd#brlt_ContractWithCustomerResizingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_brlt_ContractWithCustomerResizingPeriod_01d5aefa-d72b-4e82-aebe-6fbb1f5ccdcc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContractWithCustomerExtendedServicePlanPeriod_a10e6afa-5ca7-448a-924a-10d237203f68" xlink:href="brlt-20210930.xsd#brlt_ContractWithCustomerExtendedServicePlanPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_brlt_ContractWithCustomerExtendedServicePlanPeriod_a10e6afa-5ca7-448a-924a-10d237203f68" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_9aace052-f97d-47a8-b464-cb621eb6220f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_ContractWithCustomerLiability_9aace052-f97d-47a8-b464-cb621eb6220f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b954631c-e845-4e54-8626-8ea441812acf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b954631c-e845-4e54-8626-8ea441812acf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerRefundLiabilityCurrent_d06a21ab-c434-44f2-a2c0-b5aadb6e699f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerRefundLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_ContractWithCustomerRefundLiabilityCurrent_d06a21ab-c434-44f2-a2c0-b5aadb6e699f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_5a07a604-3aaf-4a9d-97e6-611c2cebd5bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_5a07a604-3aaf-4a9d-97e6-611c2cebd5bf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketingAndAdvertisingExpense_4b4e5d17-8f26-4d2d-8691-24c96291bea7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketingAndAdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_MarketingAndAdvertisingExpense_4b4e5d17-8f26-4d2d-8691-24c96291bea7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestTable_4786c105-d67d-48ed-873a-472aa2d857fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_5d7c4f2a-0a69-4895-9d6d-f5e68242fec5" xlink:to="loc_us-gaap_MinorityInterestTable_4786c105-d67d-48ed-873a-472aa2d857fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_7438ced9-e981-496f-9f17-31a3606cb5e1" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_4786c105-d67d-48ed-873a-472aa2d857fa" xlink:to="loc_srt_OwnershipAxis_7438ced9-e981-496f-9f17-31a3606cb5e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_7438ced9-e981-496f-9f17-31a3606cb5e1_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_7438ced9-e981-496f-9f17-31a3606cb5e1" xlink:to="loc_srt_OwnershipDomain_7438ced9-e981-496f-9f17-31a3606cb5e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_03cee5ae-4a12-4c31-bce6-b1e4ecabc1a5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_7438ced9-e981-496f-9f17-31a3606cb5e1" xlink:to="loc_srt_OwnershipDomain_03cee5ae-4a12-4c31-bce6-b1e4ecabc1a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_82b7b892-ee93-4f49-8310-f53db1376ef5" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_03cee5ae-4a12-4c31-bce6-b1e4ecabc1a5" xlink:to="loc_brlt_BrilliantEarthLLCMember_82b7b892-ee93-4f49-8310-f53db1376ef5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_91338174-e1e4-4361-9ce7-340c059bcb43" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_4786c105-d67d-48ed-873a-472aa2d857fa" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_91338174-e1e4-4361-9ce7-340c059bcb43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_91338174-e1e4-4361-9ce7-340c059bcb43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_91338174-e1e4-4361-9ce7-340c059bcb43" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_91338174-e1e4-4361-9ce7-340c059bcb43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_6a7a6137-db3a-4292-b0b4-d8a38fa5fc93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_91338174-e1e4-4361-9ce7-340c059bcb43" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_6a7a6137-db3a-4292-b0b4-d8a38fa5fc93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassPWarrantsMember_cc5a202e-df56-4854-857e-4d23a5283535" xlink:href="brlt-20210930.xsd#brlt_ClassPWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_6a7a6137-db3a-4292-b0b4-d8a38fa5fc93" xlink:to="loc_brlt_ClassPWarrantsMember_cc5a202e-df56-4854-857e-4d23a5283535" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/SummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#SummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/SummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails" xlink:type="extended" id="i013dcf4ae49440b7a539029144ff3cea_SummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_afcfae04-41e5-4d34-9ae2-bec303bd1c20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_0ffe4c11-0270-4110-9eac-44dd384e1014" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_afcfae04-41e5-4d34-9ae2-bec303bd1c20" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_0ffe4c11-0270-4110-9eac-44dd384e1014" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_71904c17-ac6a-4778-b63e-8ee5ea7582b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_afcfae04-41e5-4d34-9ae2-bec303bd1c20" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_71904c17-ac6a-4778-b63e-8ee5ea7582b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_cf619724-8cf0-42d1-bf4a-8df1183acbe8" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_71904c17-ac6a-4778-b63e-8ee5ea7582b4" xlink:to="loc_srt_StatementGeographicalAxis_cf619724-8cf0-42d1-bf4a-8df1183acbe8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_cf619724-8cf0-42d1-bf4a-8df1183acbe8_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_cf619724-8cf0-42d1-bf4a-8df1183acbe8" xlink:to="loc_srt_SegmentGeographicalDomain_cf619724-8cf0-42d1-bf4a-8df1183acbe8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_41e03ef4-81a0-42fe-9db3-5a741e1936d9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_cf619724-8cf0-42d1-bf4a-8df1183acbe8" xlink:to="loc_srt_SegmentGeographicalDomain_41e03ef4-81a0-42fe-9db3-5a741e1936d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_e37c0f8e-4466-4086-af75-b819e52c14a6" xlink:href="https://xbrl.sec.gov/country/2021/country-2021.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_41e03ef4-81a0-42fe-9db3-5a741e1936d9" xlink:to="loc_country_US_e37c0f8e-4466-4086-af75-b819e52c14a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_284fd7c2-05cf-4289-b9d6-4128199e4353" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_41e03ef4-81a0-42fe-9db3-5a741e1936d9" xlink:to="loc_us-gaap_NonUsMember_284fd7c2-05cf-4289-b9d6-4128199e4353" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/EarningsPerShareDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#EarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/EarningsPerShareDetails" xlink:type="extended" id="i17ae49b8f98f48a092500b8ed62932eb_EarningsPerShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_87b932c5-a727-42d2-b752-e6e72ed0d8d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_NetIncomeLoss_87b932c5-a727-42d2-b752-e6e72ed0d8d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_1b96d9e3-2624-4788-a7ed-cdd4e4278684" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_1b96d9e3-2624-4788-a7ed-cdd4e4278684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_d5ba622a-df95-4582-93e9-a9247d96a5f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_d5ba622a-df95-4582-93e9-a9247d96a5f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_IncomeTaxExpenseBenefitPortionAttributableToNoncontrollingInterest_374fb6dc-d654-4680-8040-e159b288a047" xlink:href="brlt-20210930.xsd#brlt_IncomeTaxExpenseBenefitPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_brlt_IncomeTaxExpenseBenefitPortionAttributableToNoncontrollingInterest_374fb6dc-d654-4680-8040-e159b288a047" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_2407fef5-3d93-4f80-b3f7-5e8e4c19faf8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_2407fef5-3d93-4f80-b3f7-5e8e4c19faf8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_9c9bd6ec-660c-459f-be52-3222dfeddefc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_9c9bd6ec-660c-459f-be52-3222dfeddefc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_0359de94-aa35-423c-b6b9-a531730d359c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_0359de94-aa35-423c-b6b9-a531730d359c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_10f0a6f3-7b9c-4e69-bbd1-86113bbb74f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_10f0a6f3-7b9c-4e69-bbd1-86113bbb74f2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_d53c4ecf-985a-47e3-90a6-35d3f47ac6ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_EarningsPerShareBasic_d53c4ecf-985a-47e3-90a6-35d3f47ac6ff" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_7c931b26-adb5-42dd-97a9-44bb0bae16e0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_EarningsPerShareDiluted_7c931b26-adb5-42dd-97a9-44bb0bae16e0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b184f61b-00a9-4f22-b4f9-b710a74313f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b184f61b-00a9-4f22-b4f9-b710a74313f4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5529ba12-e2ce-4dcc-b2ef-08cfc07e5e09" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_fce3e3a7-841a-4ca4-808e-dd9d324b853f" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5529ba12-e2ce-4dcc-b2ef-08cfc07e5e09" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5529ba12-e2ce-4dcc-b2ef-08cfc07e5e09" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_adee13a2-d24e-45b3-8461-c52b80db779a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6a3e2fc6-744e-4634-8f8b-7a15e2e77a12" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_adee13a2-d24e-45b3-8461-c52b80db779a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsExchangeableForCommonStockMember_4575d833-4493-4709-812e-e01842e0d07f" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsExchangeableForCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_adee13a2-d24e-45b3-8461-c52b80db779a" xlink:to="loc_brlt_LLCUnitsExchangeableForCommonStockMember_4575d833-4493-4709-812e-e01842e0d07f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_93cd61f0-faa2-4eba-91d0-c65a47185bd6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_adee13a2-d24e-45b3-8461-c52b80db779a" xlink:to="loc_us-gaap_StockCompensationPlanMember_93cd61f0-faa2-4eba-91d0-c65a47185bd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_8535e9b3-ee00-4b94-afcc-e3cd7689ef22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_adee13a2-d24e-45b3-8461-c52b80db779a" xlink:to="loc_us-gaap_EmployeeStockOptionMember_8535e9b3-ee00-4b94-afcc-e3cd7689ef22" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/InventoriesNetScheduleofInventoriesNetDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#InventoriesNetScheduleofInventoriesNetDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/InventoriesNetScheduleofInventoriesNetDetails" xlink:type="extended" id="i7980e0a3c44d4c12966ad753fbb8d4ec_InventoriesNetScheduleofInventoriesNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_269e5e16-162e-4a9c-a84e-906142b06290" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryGross_3878bdf1-c99a-417e-8084-74b42d7598ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_269e5e16-162e-4a9c-a84e-906142b06290" xlink:to="loc_us-gaap_InventoryGross_3878bdf1-c99a-417e-8084-74b42d7598ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryValuationReserves_69160cb3-6d75-45db-95a4-624785c88674" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryValuationReserves"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_269e5e16-162e-4a9c-a84e-906142b06290" xlink:to="loc_us-gaap_InventoryValuationReserves_69160cb3-6d75-45db-95a4-624785c88674" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_1e776e01-8ad3-41f6-9022-949e08c13913" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_269e5e16-162e-4a9c-a84e-906142b06290" xlink:to="loc_us-gaap_InventoryNet_1e776e01-8ad3-41f6-9022-949e08c13913" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_4c51eb04-29ca-4dec-a39c-385278d49f0f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryCurrentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_269e5e16-162e-4a9c-a84e-906142b06290" xlink:to="loc_us-gaap_InventoryCurrentTable_4c51eb04-29ca-4dec-a39c-385278d49f0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryAxis_a513f7ff-9e8d-4ebe-abf4-ccb772312b42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_4c51eb04-29ca-4dec-a39c-385278d49f0f" xlink:to="loc_us-gaap_PublicUtilitiesInventoryAxis_a513f7ff-9e8d-4ebe-abf4-ccb772312b42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_a513f7ff-9e8d-4ebe-abf4-ccb772312b42_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_a513f7ff-9e8d-4ebe-abf4-ccb772312b42" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_a513f7ff-9e8d-4ebe-abf4-ccb772312b42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_4d4a5c1b-ad81-4e67-9a68-87872b3dec67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_a513f7ff-9e8d-4ebe-abf4-ccb772312b42" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_4d4a5c1b-ad81-4e67-9a68-87872b3dec67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LooseDiamondsMember_d157642a-d9c5-4952-ac0c-fe631fa6d732" xlink:href="brlt-20210930.xsd#brlt_LooseDiamondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_4d4a5c1b-ad81-4e67-9a68-87872b3dec67" xlink:to="loc_brlt_LooseDiamondsMember_d157642a-d9c5-4952-ac0c-fe631fa6d732" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_FineJewelryAndOtherMember_be8da7de-3b4e-41c6-b7b9-bbf0e14bb753" xlink:href="brlt-20210930.xsd#brlt_FineJewelryAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_4d4a5c1b-ad81-4e67-9a68-87872b3dec67" xlink:to="loc_brlt_FineJewelryAndOtherMember_be8da7de-3b4e-41c6-b7b9-bbf0e14bb753" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/LongTermDebtTermLoanDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#LongTermDebtTermLoanDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/LongTermDebtTermLoanDetails" xlink:type="extended" id="i01006961d2e54ba7bfed09fd8300327a_LongTermDebtTermLoanDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_82d43596-2d9c-4346-a5f3-5435db015b2d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_82d43596-2d9c-4346-a5f3-5435db015b2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_e97dd222-2cfa-45a9-a695-975f68e3a01a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_e97dd222-2cfa-45a9-a695-975f68e3a01a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_431ec9a1-888d-4091-b394-a6a6157b5da6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_LongTermDebt_431ec9a1-888d-4091-b394-a6a6157b5da6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_c3108f67-a886-4b73-bf74-2d682fc8a6eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_LongTermDebtCurrent_c3108f67-a886-4b73-bf74-2d682fc8a6eb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LongTermDebtExcludingCurrentMaturitiesGross_2b5e9ba8-8d7e-4786-a474-2502f82a8de7" xlink:href="brlt-20210930.xsd#brlt_LongTermDebtExcludingCurrentMaturitiesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_brlt_LongTermDebtExcludingCurrentMaturitiesGross_2b5e9ba8-8d7e-4786-a474-2502f82a8de7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_efdbc0e5-2b87-41be-9bfd-b00429e363fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_efdbc0e5-2b87-41be-9bfd-b00429e363fd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_bae0b6d1-3e70-4ab7-bbfd-0a33c15da1a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_156129a4-4c03-42e7-9362-d6f61b57449a" xlink:to="loc_us-gaap_DebtInstrumentTable_bae0b6d1-3e70-4ab7-bbfd-0a33c15da1a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_c4633122-5a04-4538-9b9c-4bd09c0b8ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_bae0b6d1-3e70-4ab7-bbfd-0a33c15da1a4" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_c4633122-5a04-4538-9b9c-4bd09c0b8ba4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c4633122-5a04-4538-9b9c-4bd09c0b8ba4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c4633122-5a04-4538-9b9c-4bd09c0b8ba4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c4633122-5a04-4538-9b9c-4bd09c0b8ba4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_bca8ad80-10a6-42fb-a763-1c58b61b089d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c4633122-5a04-4538-9b9c-4bd09c0b8ba4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_bca8ad80-10a6-42fb-a763-1c58b61b089d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_656ec691-5ea0-4284-b3a0-7ca691f6ed31" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_bca8ad80-10a6-42fb-a763-1c58b61b089d" xlink:to="loc_us-gaap_SecuredDebtMember_656ec691-5ea0-4284-b3a0-7ca691f6ed31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_55d806b2-1b44-4822-ac23-c2135ee1bd79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_bae0b6d1-3e70-4ab7-bbfd-0a33c15da1a4" xlink:to="loc_us-gaap_DebtInstrumentAxis_55d806b2-1b44-4822-ac23-c2135ee1bd79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_55d806b2-1b44-4822-ac23-c2135ee1bd79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_55d806b2-1b44-4822-ac23-c2135ee1bd79" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_55d806b2-1b44-4822-ac23-c2135ee1bd79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f51c77d7-000e-49dd-afcb-32df9afd8596" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_55d806b2-1b44-4822-ac23-c2135ee1bd79" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f51c77d7-000e-49dd-afcb-32df9afd8596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TermLoanAgreementMember_626ae3bf-924b-4a50-9d58-3137fb8b6ad0" xlink:href="brlt-20210930.xsd#brlt_TermLoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_f51c77d7-000e-49dd-afcb-32df9afd8596" xlink:to="loc_brlt_TermLoanAgreementMember_626ae3bf-924b-4a50-9d58-3137fb8b6ad0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/LongTermDebtNarrativeDetails" xlink:type="extended" id="i0c2b3d1e3761470da09912609e6003c2_LongTermDebtNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_6b7f918e-443e-415c-9fec-e64937a9d9c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_6b7f918e-443e-415c-9fec-e64937a9d9c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentFloorInterestRate_28ad91ee-2b3e-4e60-b4a3-6b56f5ba5772" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentFloorInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentFloorInterestRate_28ad91ee-2b3e-4e60-b4a3-6b56f5ba5772" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_0ef8d854-6b98-43d9-ac24-411a9ccb1245" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_0ef8d854-6b98-43d9-ac24-411a9ccb1245" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentPrepaymentFeePercent_1507ff9d-141c-481a-a594-8b4a17388d25" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentPrepaymentFeePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentPrepaymentFeePercent_1507ff9d-141c-481a-a594-8b4a17388d25" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_618d48e1-3a1f-433f-8feb-33200746451e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_618d48e1-3a1f-433f-8feb-33200746451e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid_25a26715-8286-4193-9c01-870bb8db1d32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid_25a26715-8286-4193-9c01-870bb8db1d32" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_d6bf170b-c0a3-414f-b0f5-d661f1ce691f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_d6bf170b-c0a3-414f-b0f5-d661f1ce691f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_WarrantLiabilityFairValueDisclosure_51e772fa-206e-4637-b062-cfa192062d6e" xlink:href="brlt-20210930.xsd#brlt_WarrantLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_WarrantLiabilityFairValueDisclosure_51e772fa-206e-4637-b062-cfa192062d6e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassOfWarrantOrRightCarryingValue_cf2b0c74-5de6-4f11-a1ae-29ecf748842d" xlink:href="brlt-20210930.xsd#brlt_ClassOfWarrantOrRightCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_ClassOfWarrantOrRightCarryingValue_cf2b0c74-5de6-4f11-a1ae-29ecf748842d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_941655ce-47b2-485c-a62f-44a4dc2dbc45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_941655ce-47b2-485c-a62f-44a4dc2dbc45" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentMaximumDistributionPeriod_7bb06be2-c449-456d-b49d-37b6e4faf7ce" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentMaximumDistributionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentMaximumDistributionPeriod_7bb06be2-c449-456d-b49d-37b6e4faf7ce" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentVariableRateFloor_df9cfce2-113b-402d-8e28-4a65cfb654f6" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentVariableRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentVariableRateFloor_df9cfce2-113b-402d-8e28-4a65cfb654f6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_4d44f360-0460-4766-99bb-e891aa4a4438" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_4d44f360-0460-4766-99bb-e891aa4a4438" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentInterestOnlyPeriodExtension_87d67222-e9ff-4a39-b399-b4b04bd76144" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentInterestOnlyPeriodExtension"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentInterestOnlyPeriodExtension_87d67222-e9ff-4a39-b399-b4b04bd76144" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentPrepaymentTermExtension_7c1f0070-313e-4963-a14b-64f1195d29fa" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentPrepaymentTermExtension"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentPrepaymentTermExtension_7c1f0070-313e-4963-a14b-64f1195d29fa" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationPrincipal_4b9a24bf-6bf4-4d39-afc0-8cee1ebbfa8a" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationPrincipal_4b9a24bf-6bf4-4d39-afc0-8cee1ebbfa8a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationDebtIssuanceCosts_5f77188c-cb98-47c7-9c2a-9f4b744f51b3" xlink:href="brlt-20210930.xsd#brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaidModificationDebtIssuanceCosts_5f77188c-cb98-47c7-9c2a-9f4b744f51b3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassOfWarrantOrRightIssued_70ecc252-1119-4aed-a2d9-8ae77217d99d" xlink:href="brlt-20210930.xsd#brlt_ClassOfWarrantOrRightIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_brlt_ClassOfWarrantOrRightIssued_70ecc252-1119-4aed-a2d9-8ae77217d99d" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_c97d07c4-e527-49d0-b185-ef522ccc4a1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_c97d07c4-e527-49d0-b185-ef522ccc4a1e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_5c8b3cdf-0535-488d-80b2-4487ef8b2d19" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_5c8b3cdf-0535-488d-80b2-4487ef8b2d19" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_2ee76fe1-a671-4f19-95e0-39cd7123c8d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_2ee76fe1-a671-4f19-95e0-39cd7123c8d2" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_0e8b9fe7-07a3-4184-a814-e7ab46775939" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_0e8b9fe7-07a3-4184-a814-e7ab46775939" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2abdbf7a-e0ba-4c25-abf2-b834adc2211c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2abdbf7a-e0ba-4c25-abf2-b834adc2211c" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_1b704ce5-c9ef-4f08-9298-db62ed9e3280" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_InterestExpenseDebt_1b704ce5-c9ef-4f08-9298-db62ed9e3280" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_6c0d2324-b47f-422f-a8b4-2beb91b4d4c5" xlink:to="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1808d9b4-a5bd-4bf2-88da-3e48996346d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:to="loc_us-gaap_DebtInstrumentAxis_1808d9b4-a5bd-4bf2-88da-3e48996346d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1808d9b4-a5bd-4bf2-88da-3e48996346d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1808d9b4-a5bd-4bf2-88da-3e48996346d5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1808d9b4-a5bd-4bf2-88da-3e48996346d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ff772cd5-f743-4133-af94-abfdf44681c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1808d9b4-a5bd-4bf2-88da-3e48996346d5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ff772cd5-f743-4133-af94-abfdf44681c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TermLoanAgreementMember_191f3160-4cbe-401c-8f9a-6ccdf2fdadee" xlink:href="brlt-20210930.xsd#brlt_TermLoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff772cd5-f743-4133-af94-abfdf44681c9" xlink:to="loc_brlt_TermLoanAgreementMember_191f3160-4cbe-401c-8f9a-6ccdf2fdadee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_FirstTrancheTermLoanMember_248b49c4-e3bd-4856-9613-b14d2e4d2f5b" xlink:href="brlt-20210930.xsd#brlt_FirstTrancheTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_brlt_TermLoanAgreementMember_191f3160-4cbe-401c-8f9a-6ccdf2fdadee" xlink:to="loc_brlt_FirstTrancheTermLoanMember_248b49c4-e3bd-4856-9613-b14d2e4d2f5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_SecondTrancheTermLoanMember_bf7a069a-9bb4-488a-9378-3dd0df0118a1" xlink:href="brlt-20210930.xsd#brlt_SecondTrancheTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_brlt_TermLoanAgreementMember_191f3160-4cbe-401c-8f9a-6ccdf2fdadee" xlink:to="loc_brlt_SecondTrancheTermLoanMember_bf7a069a-9bb4-488a-9378-3dd0df0118a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_PayrollProtectionProgramLoanCARESActMember_f0a7c7ec-9aa3-4267-9c27-25919fc53315" xlink:href="brlt-20210930.xsd#brlt_PayrollProtectionProgramLoanCARESActMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff772cd5-f743-4133-af94-abfdf44681c9" xlink:to="loc_brlt_PayrollProtectionProgramLoanCARESActMember_f0a7c7ec-9aa3-4267-9c27-25919fc53315" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a3a314bb-6a07-49b6-92a0-3def71cd3c55" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a3a314bb-6a07-49b6-92a0-3def71cd3c55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a3a314bb-6a07-49b6-92a0-3def71cd3c55_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a3a314bb-6a07-49b6-92a0-3def71cd3c55" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a3a314bb-6a07-49b6-92a0-3def71cd3c55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7f53812a-05e7-42a8-99b0-0be883b2ec6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a3a314bb-6a07-49b6-92a0-3def71cd3c55" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7f53812a-05e7-42a8-99b0-0be883b2ec6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_0c2edca2-ca28-4924-abb4-04bc8ef566b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_7f53812a-05e7-42a8-99b0-0be883b2ec6e" xlink:to="loc_us-gaap_SecuredDebtMember_0c2edca2-ca28-4924-abb4-04bc8ef566b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:to="loc_us-gaap_VariableRateAxis_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8" xlink:to="loc_us-gaap_VariableRateDomain_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_6755da61-2c43-4d54-9f7e-77f9bbc39acf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_4ab29c8d-5c44-4d5c-bfb9-afe41638b2d8" xlink:to="loc_us-gaap_VariableRateDomain_6755da61-2c43-4d54-9f7e-77f9bbc39acf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_14460d24-284e-4d02-a8e7-6ae3ee990642" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_6755da61-2c43-4d54-9f7e-77f9bbc39acf" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_14460d24-284e-4d02-a8e7-6ae3ee990642" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e05e56f3-851c-42a1-8277-743a52f680d5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:to="loc_srt_RangeAxis_e05e56f3-851c-42a1-8277-743a52f680d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e05e56f3-851c-42a1-8277-743a52f680d5_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e05e56f3-851c-42a1-8277-743a52f680d5" xlink:to="loc_srt_RangeMember_e05e56f3-851c-42a1-8277-743a52f680d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e3717d14-2031-48d1-8d8b-ad68e996a25c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e05e56f3-851c-42a1-8277-743a52f680d5" xlink:to="loc_srt_RangeMember_e3717d14-2031-48d1-8d8b-ad68e996a25c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ec2d9e1a-b90b-4207-b6c1-9a6e06e4282e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e3717d14-2031-48d1-8d8b-ad68e996a25c" xlink:to="loc_srt_MaximumMember_ec2d9e1a-b90b-4207-b6c1-9a6e06e4282e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_adabc64c-47a8-4a1c-a44a-95b899b3b3dd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e3717d14-2031-48d1-8d8b-ad68e996a25c" xlink:to="loc_srt_MinimumMember_adabc64c-47a8-4a1c-a44a-95b899b3b3dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_e4845e8e-02d2-4ca8-9a40-dfffb74d377e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_46c60c90-5201-4889-a8c8-d4c7cfbf0302" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_e4845e8e-02d2-4ca8-9a40-dfffb74d377e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_e4845e8e-02d2-4ca8-9a40-dfffb74d377e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_e4845e8e-02d2-4ca8-9a40-dfffb74d377e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_e4845e8e-02d2-4ca8-9a40-dfffb74d377e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_f54db0f7-0068-4108-bc9e-4eab6cdfd926" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_e4845e8e-02d2-4ca8-9a40-dfffb74d377e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_f54db0f7-0068-4108-bc9e-4eab6cdfd926" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassPWarrantsMember_f271790f-5b45-45c9-9c98-41067fd5b8dd" xlink:href="brlt-20210930.xsd#brlt_ClassPWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_f54db0f7-0068-4108-bc9e-4eab6cdfd926" xlink:to="loc_brlt_ClassPWarrantsMember_f271790f-5b45-45c9-9c98-41067fd5b8dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_FirstAmendmentWarrantsMember_9e27caf6-8f1f-45b1-bd44-02804aee9e35" xlink:href="brlt-20210930.xsd#brlt_FirstAmendmentWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_f54db0f7-0068-4108-bc9e-4eab6cdfd926" xlink:to="loc_brlt_FirstAmendmentWarrantsMember_9e27caf6-8f1f-45b1-bd44-02804aee9e35" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/StockholdersandMembersEquityScheduleofCapitalizationDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#StockholdersandMembersEquityScheduleofCapitalizationDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/StockholdersandMembersEquityScheduleofCapitalizationDetails" xlink:type="extended" id="i84b81653d8f24883945217b59f18f900_StockholdersandMembersEquityScheduleofCapitalizationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_785c0476-c10e-4b68-a434-ac22a087451f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_785c0476-c10e-4b68-a434-ac22a087451f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_3d269509-4b1f-4ea2-8026-291848c474fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_3d269509-4b1f-4ea2-8026-291848c474fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_7130dbab-deff-4eff-9b5b-cda1d085fe90" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_PreferredStockSharesIssued_7130dbab-deff-4eff-9b5b-cda1d085fe90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_6198309a-f6ff-4629-898e-9d8b26de1d22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_6198309a-f6ff-4629-898e-9d8b26de1d22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_b4dbdd0e-45a9-4008-9d03-ff40b3511e1b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonStockSharesIssued_b4dbdd0e-45a9-4008-9d03-ff40b3511e1b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_6567f5e7-fb5d-40ea-ba2f-bc642b35f1e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_6567f5e7-fb5d-40ea-ba2f-bc642b35f1e8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonStockVotesPerShare_90db107a-53d2-4062-b868-1157971497a1" xlink:href="brlt-20210930.xsd#brlt_CommonStockVotesPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_brlt_CommonStockVotesPerShare_90db107a-53d2-4062-b868-1157971497a1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_8179b189-2341-4ab1-8500-6f09577dc7ca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_8179b189-2341-4ab1-8500-6f09577dc7ca" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitIssued_1265dca3-e3b8-4c08-858c-0a4b49b8c34f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonUnitIssued_1265dca3-e3b8-4c08-858c-0a4b49b8c34f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_a864a409-89c4-4c19-8c12-fbe43c37a680" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_CommonUnitOutstanding_a864a409-89c4-4c19-8c12-fbe43c37a680" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_5d09c2e3-6321-41fe-b213-0a55b3c4e25b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_350a6279-887a-40ee-bba8-8c5c6bb463f7" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_5d09c2e3-6321-41fe-b213-0a55b3c4e25b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_757cb0b2-d467-4ec6-8274-0e1b533586a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5d09c2e3-6321-41fe-b213-0a55b3c4e25b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_757cb0b2-d467-4ec6-8274-0e1b533586a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_757cb0b2-d467-4ec6-8274-0e1b533586a4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_757cb0b2-d467-4ec6-8274-0e1b533586a4" xlink:to="loc_us-gaap_ClassOfStockDomain_757cb0b2-d467-4ec6-8274-0e1b533586a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_757cb0b2-d467-4ec6-8274-0e1b533586a4" xlink:to="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_fe40ce6b-8915-4568-8e7f-34523ffcc6e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:to="loc_us-gaap_CommonClassAMember_fe40ce6b-8915-4568-8e7f-34523ffcc6e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_f2a592ee-0249-4a34-90fd-75798b98fe61" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:to="loc_us-gaap_CommonClassBMember_f2a592ee-0249-4a34-90fd-75798b98fe61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_baec177c-7138-4365-a8c4-1006475e2251" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:to="loc_us-gaap_CommonClassCMember_baec177c-7138-4365-a8c4-1006475e2251" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonClassDMember_be6c028d-5393-42fd-a93b-19970e9111a4" xlink:href="brlt-20210930.xsd#brlt_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a8e9110e-fab3-4f93-8cb8-7a5c2ba8ecf0" xlink:to="loc_brlt_CommonClassDMember_be6c028d-5393-42fd-a93b-19970e9111a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_7626a638-8f5d-47f5-b19c-17eeac4e4285" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5d09c2e3-6321-41fe-b213-0a55b3c4e25b" xlink:to="loc_us-gaap_AwardTypeAxis_7626a638-8f5d-47f5-b19c-17eeac4e4285" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7626a638-8f5d-47f5-b19c-17eeac4e4285_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_7626a638-8f5d-47f5-b19c-17eeac4e4285" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7626a638-8f5d-47f5-b19c-17eeac4e4285_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_7626a638-8f5d-47f5-b19c-17eeac4e4285" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsConvertedMember_90cee9ef-53b3-405a-87c0-0dc7c0f01892" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsConvertedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:to="loc_brlt_LLCUnitsConvertedMember_90cee9ef-53b3-405a-87c0-0dc7c0f01892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsVestedMember_660e8d80-0f79-4f56-8c6f-388d489ff92e" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsVestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:to="loc_brlt_LLCUnitsVestedMember_660e8d80-0f79-4f56-8c6f-388d489ff92e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_6d35866f-7325-4ca1-b43a-84e8f43bdb42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_6d35866f-7325-4ca1-b43a-84e8f43bdb42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_61ed0a57-7fb4-402e-a0b0-c9169ed825c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_103e8932-113a-47ef-85c7-bbc158c2c60f" xlink:to="loc_us-gaap_EmployeeStockOptionMember_61ed0a57-7fb4-402e-a0b0-c9169ed825c4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/StockholdersandMembersEquityNarrativeDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#StockholdersandMembersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/StockholdersandMembersEquityNarrativeDetails" xlink:type="extended" id="i73c9aa4d170744eb9d30c054136c00dc_StockholdersandMembersEquityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_f2ba6faf-636a-48d8-86e9-46a4af26baad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_PreferredStockSharesIssued_f2ba6faf-636a-48d8-86e9-46a4af26baad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitationOnIssuanceOfCommonStockRatioOfCommonStockRequiredToBeHeldToNumberOfLLCInterestsHeld_e36559a6-c601-43e3-8904-eff5f724c4d2" xlink:href="brlt-20210930.xsd#brlt_LimitationOnIssuanceOfCommonStockRatioOfCommonStockRequiredToBeHeldToNumberOfLLCInterestsHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_brlt_LimitationOnIssuanceOfCommonStockRatioOfCommonStockRequiredToBeHeldToNumberOfLLCInterestsHeld_e36559a6-c601-43e3-8904-eff5f724c4d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_5e6b79ba-47b1-4eb5-ab1e-69b898bbe049" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_CommonStockSharesIssued_5e6b79ba-47b1-4eb5-ab1e-69b898bbe049" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_005ca057-e312-4fd9-a35d-217d8f28275b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_005ca057-e312-4fd9-a35d-217d8f28275b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_f5027718-af75-48d8-909e-cf674a903d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_f5027718-af75-48d8-909e-cf674a903d8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_725b0228-bee1-44f1-b36c-fb97efa676e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_725b0228-bee1-44f1-b36c-fb97efa676e1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest_50356550-6add-41e4-8e91-72424ab89d3c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest_50356550-6add-41e4-8e91-72424ab89d3c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_848ab88b-26fc-4b8b-aedd-41f0ac5bf041" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_848ab88b-26fc-4b8b-aedd-41f0ac5bf041" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ConversionOfStockAwardsConversionRatio_608d7e35-ae32-4c5f-a0fc-e514ea1ede65" xlink:href="brlt-20210930.xsd#brlt_ConversionOfStockAwardsConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_brlt_ConversionOfStockAwardsConversionRatio_608d7e35-ae32-4c5f-a0fc-e514ea1ede65" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f7bff524-8007-4e7e-8dde-7c557b8d5633" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f7bff524-8007-4e7e-8dde-7c557b8d5633" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_38888051-0650-49bd-bd44-e4663d4d6750" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_38888051-0650-49bd-bd44-e4663d4d6750" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_10afbd60-282d-4c05-bed7-d1351b84e1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_10afbd60-282d-4c05-bed7-d1351b84e1cf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDistributionsToAffiliates_072d3682-6d3b-499c-b5b2-cda4b4ec7a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDistributionsToAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_PaymentsOfDistributionsToAffiliates_072d3682-6d3b-499c-b5b2-cda4b4ec7a7b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_34cd8b52-84e0-490f-bd0d-d3cb2bd42cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityEliminationAsPartofReorganization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_34cd8b52-84e0-490f-bd0d-d3cb2bd42cd3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_1f2ba9da-796d-4379-ae56-d0d1a75606a5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_1f2ba9da-796d-4379-ae56-d0d1a75606a5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_d67a4321-348d-4368-bb74-2b533420015f" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6" xlink:to="loc_us-gaap_ClassOfStockDomain_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a0ef1515-7b8d-41f9-9d1c-0ac3163a4ba6" xlink:to="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_dbe26024-5ef6-45ee-9d50-8974ed68653b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:to="loc_us-gaap_CommonClassAMember_dbe26024-5ef6-45ee-9d50-8974ed68653b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonClassBAndClassCMember_46e48220-8ee1-41eb-9201-94d6a857d989" xlink:href="brlt-20210930.xsd#brlt_CommonClassBAndClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:to="loc_brlt_CommonClassBAndClassCMember_46e48220-8ee1-41eb-9201-94d6a857d989" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_80c4e7aa-3d8b-4b22-8fb9-87a206595cf7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:to="loc_us-gaap_CommonClassBMember_80c4e7aa-3d8b-4b22-8fb9-87a206595cf7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_d13929dd-7046-471d-b5bc-d877eb3b0249" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:to="loc_us-gaap_CommonClassCMember_d13929dd-7046-471d-b5bc-d877eb3b0249" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_CommonClassDMember_2f21a171-cc39-405b-b5ea-5f96d3b68292" xlink:href="brlt-20210930.xsd#brlt_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50f33d64-47b7-4994-b568-5acf9f8d46dd" xlink:to="loc_brlt_CommonClassDMember_2f21a171-cc39-405b-b5ea-5f96d3b68292" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_22ef9bce-5ea2-4002-8095-b7224e51137e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_srt_CounterpartyNameAxis_22ef9bce-5ea2-4002-8095-b7224e51137e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_22ef9bce-5ea2-4002-8095-b7224e51137e_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_22ef9bce-5ea2-4002-8095-b7224e51137e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_22ef9bce-5ea2-4002-8095-b7224e51137e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_50da4fa2-c1ad-47e3-81be-6c40002066bf" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_22ef9bce-5ea2-4002-8095-b7224e51137e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_50da4fa2-c1ad-47e3-81be-6c40002066bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_IPOInvestorsMember_d57a2c10-e804-4681-a0c7-e7562b952bd4" xlink:href="brlt-20210930.xsd#brlt_IPOInvestorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_50da4fa2-c1ad-47e3-81be-6c40002066bf" xlink:to="loc_brlt_IPOInvestorsMember_d57a2c10-e804-4681-a0c7-e7562b952bd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContinuingEquityOwnersMember_00ae0b2f-f0cb-4663-a07c-b5054b5b5212" xlink:href="brlt-20210930.xsd#brlt_ContinuingEquityOwnersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_50da4fa2-c1ad-47e3-81be-6c40002066bf" xlink:to="loc_brlt_ContinuingEquityOwnersMember_00ae0b2f-f0cb-4663-a07c-b5054b5b5212" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_FoundersMember_2c815f6c-d2bc-4364-a13c-501f9f950203" xlink:href="brlt-20210930.xsd#brlt_FoundersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_50da4fa2-c1ad-47e3-81be-6c40002066bf" xlink:to="loc_brlt_FoundersMember_2c815f6c-d2bc-4364-a13c-501f9f950203" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_srt_OwnershipAxis_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3" xlink:to="loc_srt_OwnershipDomain_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_d4c4d1c9-5e00-474a-8fe7-ba76e1b64236" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_fb4f3e9c-a729-4ba9-98bb-40b6636e3dd3" xlink:to="loc_srt_OwnershipDomain_d4c4d1c9-5e00-474a-8fe7-ba76e1b64236" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_ad85d26e-e90e-4421-9698-6e3a36121074" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_d4c4d1c9-5e00-474a-8fe7-ba76e1b64236" xlink:to="loc_brlt_BrilliantEarthLLCMember_ad85d26e-e90e-4421-9698-6e3a36121074" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_f1d2b20e-8372-440c-a720-358e81014beb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_f1d2b20e-8372-440c-a720-358e81014beb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_f1d2b20e-8372-440c-a720-358e81014beb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_f1d2b20e-8372-440c-a720-358e81014beb" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_f1d2b20e-8372-440c-a720-358e81014beb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_96634121-9fa9-4802-8773-3bb604fc234c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_f1d2b20e-8372-440c-a720-358e81014beb" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_96634121-9fa9-4802-8773-3bb604fc234c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember_b26ad428-5fce-4524-b873-7630884d74a9" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_96634121-9fa9-4802-8773-3bb604fc234c" xlink:to="loc_brlt_LLCUnitsConvertedIntoClassAAndClassDCommonStockMember_b26ad428-5fce-4524-b873-7630884d74a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_64ee3438-78b1-462e-828a-33768f3acad0" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_dei_LegalEntityAxis_64ee3438-78b1-462e-828a-33768f3acad0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_64ee3438-78b1-462e-828a-33768f3acad0_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_64ee3438-78b1-462e-828a-33768f3acad0" xlink:to="loc_dei_EntityDomain_64ee3438-78b1-462e-828a-33768f3acad0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_020e676d-790d-4f2e-9f19-4eed4c16fb37" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_64ee3438-78b1-462e-828a-33768f3acad0" xlink:to="loc_dei_EntityDomain_020e676d-790d-4f2e-9f19-4eed4c16fb37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_0bbdeadb-742b-43f9-92e9-b062728d0b32" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_020e676d-790d-4f2e-9f19-4eed4c16fb37" xlink:to="loc_brlt_BrilliantEarthLLCMember_0bbdeadb-742b-43f9-92e9-b062728d0b32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_us-gaap_VestingAxis_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a" xlink:to="loc_us-gaap_VestingDomain_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_d43a933e-22fb-4c6f-80dd-26b1673af50f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_f6dfd43c-9eab-4ebf-a21b-3faaf440f32a" xlink:to="loc_us-gaap_VestingDomain_d43a933e-22fb-4c6f-80dd-26b1673af50f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_4e5d80d2-9ded-490c-a51b-e2e2aadb343e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_d43a933e-22fb-4c6f-80dd-26b1673af50f" xlink:to="loc_us-gaap_CommonClassBMember_4e5d80d2-9ded-490c-a51b-e2e2aadb343e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_a1bc8836-7fbb-4aec-a905-1d45e0ee5250" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_807f41e9-8b0a-48eb-bea0-284c7b4a27d5" xlink:to="loc_us-gaap_AwardTypeAxis_a1bc8836-7fbb-4aec-a905-1d45e0ee5250" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a1bc8836-7fbb-4aec-a905-1d45e0ee5250_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_a1bc8836-7fbb-4aec-a905-1d45e0ee5250" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a1bc8836-7fbb-4aec-a905-1d45e0ee5250_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ae14de25-5491-4490-9c47-4d2af9aba730" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_a1bc8836-7fbb-4aec-a905-1d45e0ee5250" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ae14de25-5491-4490-9c47-4d2af9aba730" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_80cd7dd2-627a-408b-9a1a-c5ff0ef8a96b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ae14de25-5491-4490-9c47-4d2af9aba730" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_80cd7dd2-627a-408b-9a1a-c5ff0ef8a96b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/StockholdersandMembersEquityChangeinUnitsPriortoReorganizationDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#StockholdersandMembersEquityChangeinUnitsPriortoReorganizationDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/StockholdersandMembersEquityChangeinUnitsPriortoReorganizationDetails" xlink:type="extended" id="ia1b873da724c49c3a409c895b1c117b2_StockholdersandMembersEquityChangeinUnitsPriortoReorganizationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_f2fa0133-4ba3-4353-87ce-ac30bfceef6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f2fa0133-4ba3-4353-87ce-ac30bfceef6e" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_f9070027-7e8d-4104-917f-be8ce5e644f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_f9070027-7e8d-4104-917f-be8ce5e644f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_c381a4ba-0aae-4e47-9b13-27b0fde98720" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_c381a4ba-0aae-4e47-9b13-27b0fde98720" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TemporaryEquityTaxDistributionsToMembers_cf316994-2f32-468b-b08a-a286ad662920" xlink:href="brlt-20210930.xsd#brlt_TemporaryEquityTaxDistributionsToMembers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_brlt_TemporaryEquityTaxDistributionsToMembers_cf316994-2f32-468b-b08a-a286ad662920" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityNetIncome_34cd4cfe-bc29-4d79-b0e2-ebeb4b727732" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityNetIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_us-gaap_TemporaryEquityNetIncome_34cd4cfe-bc29-4d79-b0e2-ebeb4b727732" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_1c9d1598-6113-49df-a7d8-ee518a896540" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_1c9d1598-6113-49df-a7d8-ee518a896540" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TemporaryEquityEliminationAsPartOfReorganizationShares_462b48bd-6ed9-4d31-b023-e810b513b159" xlink:href="brlt-20210930.xsd#brlt_TemporaryEquityEliminationAsPartOfReorganizationShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_brlt_TemporaryEquityEliminationAsPartOfReorganizationShares_462b48bd-6ed9-4d31-b023-e810b513b159" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_70cf9788-ad5b-4c5b-92f0-966d111d8126" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityEliminationAsPartofReorganization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_796d3a48-0017-4936-99c9-72cf5eccac1d" xlink:to="loc_us-gaap_TemporaryEquityEliminationAsPartofReorganization_70cf9788-ad5b-4c5b-92f0-966d111d8126" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_2a4fc508-27db-4a07-9f4d-bbfcdae6d2f3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_599a9145-b372-4392-97d6-e8430fdc441e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f2fa0133-4ba3-4353-87ce-ac30bfceef6e" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_07ba8da0-2c16-4557-98da-ac7a5afa3f19" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_CommonUnitOutstanding_07ba8da0-2c16-4557-98da-ac7a5afa3f19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_8715c38a-04ed-481d-860a-533984c4b2af" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_MembersEquity_8715c38a-04ed-481d-860a-533984c4b2af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers_64a8858b-7980-4f7d-88a8-68e1e4df6e07" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityTaxDistributionsToMembers_64a8858b-7980-4f7d-88a8-68e1e4df6e07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares_d5a28fc3-a665-4de9-bfe6-174530b66c78" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityUnitsVestedShares_d5a28fc3-a665-4de9-bfe6-174530b66c78" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation_de56de66-b3c2-4b5c-ac5e-d5bebeb8ebb7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLLCMembersEquityUnitBasedCompensation_de56de66-b3c2-4b5c-ac5e-d5bebeb8ebb7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_e8b1dfee-9354-4772-97a3-fd04d6a470b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_ProfitLoss_e8b1dfee-9354-4772-97a3-fd04d6a470b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment_33e31bd4-aaeb-41a7-8530-6029c0f759c2" xlink:href="brlt-20210930.xsd#brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_brlt_LimitedLiabilityCompanyLLCMembersEquityAccretionToRedemptionValueAdjustment_33e31bd4-aaeb-41a7-8530-6029c0f759c2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_42ae47ac-51fb-449c-a4d6-790cb63a2beb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_42ae47ac-51fb-449c-a4d6-790cb63a2beb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_c369fc1f-7a22-4bf4-97c5-7756e1e421e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_50f9c95f-0e54-4bb7-bb0e-ed04f9d8c8ce" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_c369fc1f-7a22-4bf4-97c5-7756e1e421e6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_2df9f7cd-e5db-4982-b979-afc93f29fec0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_7bc5114d-7b12-49ee-ac70-54a70246d05d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MembersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_a01010fa-659c-4e53-a7e5-32d1cc785571" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_f2fa0133-4ba3-4353-87ce-ac30bfceef6e" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_a01010fa-659c-4e53-a7e5-32d1cc785571" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_5f683238-3490-4290-81f9-fd1814c80947" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_a01010fa-659c-4e53-a7e5-32d1cc785571" xlink:to="loc_us-gaap_StatementClassOfStockAxis_5f683238-3490-4290-81f9-fd1814c80947" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5f683238-3490-4290-81f9-fd1814c80947_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5f683238-3490-4290-81f9-fd1814c80947" xlink:to="loc_us-gaap_ClassOfStockDomain_5f683238-3490-4290-81f9-fd1814c80947_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9b3c10dc-5ba8-4994-afb5-a803bd4b4364" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5f683238-3490-4290-81f9-fd1814c80947" xlink:to="loc_us-gaap_ClassOfStockDomain_9b3c10dc-5ba8-4994-afb5-a803bd4b4364" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassFUnitsMember_dce0f6f7-22bd-4369-af63-a4657360a4d2" xlink:href="brlt-20210930.xsd#brlt_ClassFUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9b3c10dc-5ba8-4994-afb5-a803bd4b4364" xlink:to="loc_brlt_ClassFUnitsMember_dce0f6f7-22bd-4369-af63-a4657360a4d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassMUnitsMember_5300cc16-3712-417a-bb31-ec3a0c4659a7" xlink:href="brlt-20210930.xsd#brlt_ClassMUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9b3c10dc-5ba8-4994-afb5-a803bd4b4364" xlink:to="loc_brlt_ClassMUnitsMember_5300cc16-3712-417a-bb31-ec3a0c4659a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_39fbeae4-ce77-4b65-9ccf-0a955310e15f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_a01010fa-659c-4e53-a7e5-32d1cc785571" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_39fbeae4-ce77-4b65-9ccf-0a955310e15f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_39fbeae4-ce77-4b65-9ccf-0a955310e15f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_39fbeae4-ce77-4b65-9ccf-0a955310e15f" xlink:to="loc_us-gaap_EquityComponentDomain_39fbeae4-ce77-4b65-9ccf-0a955310e15f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_bd6b7d5d-4896-43a4-badd-3c283e472913" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_39fbeae4-ce77-4b65-9ccf-0a955310e15f" xlink:to="loc_us-gaap_EquityComponentDomain_bd6b7d5d-4896-43a4-badd-3c283e472913" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MemberUnitsMember_32c492a9-8e08-436e-b9e0-0da470e973f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MemberUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bd6b7d5d-4896-43a4-badd-3c283e472913" xlink:to="loc_us-gaap_MemberUnitsMember_32c492a9-8e08-436e-b9e0-0da470e973f1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/EquityBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#EquityBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/EquityBasedCompensationNarrativeDetails" xlink:type="extended" id="i2451187b088d49ee8370272622cf2b43_EquityBasedCompensationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_adaf730b-c9cc-4c50-b0e1-7a7a2c356012" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_adaf730b-c9cc-4c50-b0e1-7a7a2c356012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding_71c2fa92-d610-44ed-9ced-b756295a3fa4" xlink:href="brlt-20210930.xsd#brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding_71c2fa92-d610-44ed-9ced-b756295a3fa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuedUponExercise_67f4276a-e453-4e04-b6af-22e309f8c75f" xlink:href="brlt-20210930.xsd#brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuedUponExercise"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_brlt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuedUponExercise_67f4276a-e453-4e04-b6af-22e309f8c75f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_ac408b04-cac0-4a84-978d-b2a243b56d98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_ac408b04-cac0-4a84-978d-b2a243b56d98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_7b7d24f8-8965-4228-bd06-d033df678eac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_7b7d24f8-8965-4228-bd06-d033df678eac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_a376ebd7-f8ef-4010-b7ae-d27ce6120427" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_a376ebd7-f8ef-4010-b7ae-d27ce6120427" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_5f1287fa-ba1b-431d-8671-5068cdc105ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_5f1287fa-ba1b-431d-8671-5068cdc105ff" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ConversionOfStockAwardsConversionRatio_1b7b4d4a-b6b9-4eb4-bde2-81fffece92cd" xlink:href="brlt-20210930.xsd#brlt_ConversionOfStockAwardsConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_brlt_ConversionOfStockAwardsConversionRatio_1b7b4d4a-b6b9-4eb4-bde2-81fffece92cd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_83e089dd-7cbc-4364-b8d6-35d047a129c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_83e089dd-7cbc-4364-b8d6-35d047a129c9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a58155c6-75ef-42d6-859b-60fa4ca4dbbb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a58155c6-75ef-42d6-859b-60fa4ca4dbbb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_0496b539-d8c3-4eb3-bd7f-7068b4564d25" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_0496b539-d8c3-4eb3-bd7f-7068b4564d25" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_c0c9f13b-281c-4b9c-8efa-5434e8cd9f26" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_c0c9f13b-281c-4b9c-8efa-5434e8cd9f26" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_8de2ae98-6c4c-48d1-b898-c8151d90d033" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_8de2ae98-6c4c-48d1-b898-c8151d90d033" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_b87017c9-383e-498a-a676-5c77a0d1b4fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_b87017c9-383e-498a-a676-5c77a0d1b4fe" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_db633a70-da0b-4319-9ccc-ffde8908352a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_db633a70-da0b-4319-9ccc-ffde8908352a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_61c6e228-e34f-4d52-92b9-e9171f77aeab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_61c6e228-e34f-4d52-92b9-e9171f77aeab" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_cbeccba5-33fb-43ce-aeef-61b4de5c1a21" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_cbeccba5-33fb-43ce-aeef-61b4de5c1a21" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_08da9393-7e82-4b4f-9caf-7ec91d863c53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_08da9393-7e82-4b4f-9caf-7ec91d863c53" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_6b49c4a5-7770-41fc-9eca-e7bed0a898cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_6b49c4a5-7770-41fc-9eca-e7bed0a898cc" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_6a9716c7-bc0a-4821-9b49-996c066bc821" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_6a9716c7-bc0a-4821-9b49-996c066bc821" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_a24c9751-f4c7-4bc7-bd83-9f84aa58b82b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_a24c9751-f4c7-4bc7-bd83-9f84aa58b82b" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9de702d7-1998-41f7-beba-7790c62c2db7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2ed45ba7-35f5-4f28-b75f-2233500879bc" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9de702d7-1998-41f7-beba-7790c62c2db7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_087e38ae-cc5e-4ed6-800e-47a591af5a45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9de702d7-1998-41f7-beba-7790c62c2db7" xlink:to="loc_us-gaap_PlanNameAxis_087e38ae-cc5e-4ed6-800e-47a591af5a45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_087e38ae-cc5e-4ed6-800e-47a591af5a45_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_087e38ae-cc5e-4ed6-800e-47a591af5a45" xlink:to="loc_us-gaap_PlanNameDomain_087e38ae-cc5e-4ed6-800e-47a591af5a45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_3ffd73e3-2a07-4617-9658-51a055e35361" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_087e38ae-cc5e-4ed6-800e-47a591af5a45" xlink:to="loc_us-gaap_PlanNameDomain_3ffd73e3-2a07-4617-9658-51a055e35361" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_A2021IncentiveAwardPlanMember_21f14330-0f46-4b7f-be70-1ea3ac0715b8" xlink:href="brlt-20210930.xsd#brlt_A2021IncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_3ffd73e3-2a07-4617-9658-51a055e35361" xlink:to="loc_brlt_A2021IncentiveAwardPlanMember_21f14330-0f46-4b7f-be70-1ea3ac0715b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9de702d7-1998-41f7-beba-7790c62c2db7" xlink:to="loc_us-gaap_AwardTypeAxis_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_ded9e144-ecbd-4283-9ce4-ad5dda0cd3b0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_3bc008ef-759a-44f6-a068-1cf93dcaff17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:to="loc_us-gaap_EmployeeStockMember_3bc008ef-759a-44f6-a068-1cf93dcaff17" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ClassMUnitsMember_b8dd8fb1-4da7-438b-a352-59c51f2029f2" xlink:href="brlt-20210930.xsd#brlt_ClassMUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:to="loc_brlt_ClassMUnitsMember_b8dd8fb1-4da7-438b-a352-59c51f2029f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsMember_cb8356e8-cbe8-4f5d-87bf-85144260a59a" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:to="loc_brlt_LLCUnitsMember_cb8356e8-cbe8-4f5d-87bf-85144260a59a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_38c801b5-6f7a-4405-8fe9-318da534a065" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_38c801b5-6f7a-4405-8fe9-318da534a065" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_b81b22f5-d82f-45d8-ab7e-f25631dd9806" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ab659f11-7c52-422f-8526-2f168f35ebd3" xlink:to="loc_us-gaap_EmployeeStockOptionMember_b81b22f5-d82f-45d8-ab7e-f25631dd9806" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_e0163d50-38ae-4d7c-a32d-805638e7493c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9de702d7-1998-41f7-beba-7790c62c2db7" xlink:to="loc_us-gaap_VestingAxis_e0163d50-38ae-4d7c-a32d-805638e7493c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_e0163d50-38ae-4d7c-a32d-805638e7493c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_e0163d50-38ae-4d7c-a32d-805638e7493c" xlink:to="loc_us-gaap_VestingDomain_e0163d50-38ae-4d7c-a32d-805638e7493c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_79e2ad8c-1bb7-489c-9c21-ac3e8fb65877" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_e0163d50-38ae-4d7c-a32d-805638e7493c" xlink:to="loc_us-gaap_VestingDomain_79e2ad8c-1bb7-489c-9c21-ac3e8fb65877" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_072762b3-3ba0-4ef4-85a8-b89f14d65e70" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_79e2ad8c-1bb7-489c-9c21-ac3e8fb65877" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_072762b3-3ba0-4ef4-85a8-b89f14d65e70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_7a55b1a1-9797-44f9-a7e3-5841b5472264" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_79e2ad8c-1bb7-489c-9c21-ac3e8fb65877" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_7a55b1a1-9797-44f9-a7e3-5841b5472264" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/EquityBasedCompensationValuationAssumptionsDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#EquityBasedCompensationValuationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/EquityBasedCompensationValuationAssumptionsDetails" xlink:type="extended" id="i14d8381d056b49c1b6981edb17621f5c_EquityBasedCompensationValuationAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019f7327-7e4c-4106-b945-e18d4ef75fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019f7327-7e4c-4106-b945-e18d4ef75fa5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_75af1984-3c55-497e-9644-785babb4ac51" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_75af1984-3c55-497e-9644-785babb4ac51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_6bbca880-6424-457a-9798-7a9a5f48b9a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_6bbca880-6424-457a-9798-7a9a5f48b9a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a6182c5b-d6db-4d76-8b13-96f16ce5ab28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a6182c5b-d6db-4d76-8b13-96f16ce5ab28" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bead6671-3b7f-4139-b204-9b50ebed2a60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_a09a5a18-5b92-4ad5-9833-43755b4dbe14" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bead6671-3b7f-4139-b204-9b50ebed2a60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bead6671-3b7f-4139-b204-9b50ebed2a60" xlink:to="loc_us-gaap_AwardTypeAxis_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58163615-651d-4ea3-820a-7bd338b2ffda" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b0f0315c-70ea-45e8-86b2-ece87c8c6b7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58163615-651d-4ea3-820a-7bd338b2ffda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_f7e07242-031c-44c2-9db6-2ec3acc9bcf6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58163615-651d-4ea3-820a-7bd338b2ffda" xlink:to="loc_us-gaap_EmployeeStockOptionMember_f7e07242-031c-44c2-9db6-2ec3acc9bcf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_faff1be0-a0b7-442f-b8cd-989dd332b28b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bead6671-3b7f-4139-b204-9b50ebed2a60" xlink:to="loc_srt_RangeAxis_faff1be0-a0b7-442f-b8cd-989dd332b28b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_faff1be0-a0b7-442f-b8cd-989dd332b28b_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_faff1be0-a0b7-442f-b8cd-989dd332b28b" xlink:to="loc_srt_RangeMember_faff1be0-a0b7-442f-b8cd-989dd332b28b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_abdc96d4-5afa-451e-94ea-17600cae992a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_faff1be0-a0b7-442f-b8cd-989dd332b28b" xlink:to="loc_srt_RangeMember_abdc96d4-5afa-451e-94ea-17600cae992a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_59e6f372-8cd1-4407-bf9f-71abd13827a0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_abdc96d4-5afa-451e-94ea-17600cae992a" xlink:to="loc_srt_MinimumMember_59e6f372-8cd1-4407-bf9f-71abd13827a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f7bff5a6-184e-423a-bb0d-232c436f8e08" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_abdc96d4-5afa-451e-94ea-17600cae992a" xlink:to="loc_srt_MaximumMember_f7bff5a6-184e-423a-bb0d-232c436f8e08" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/EquityBasedCompensationLLCUnitActivityDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#EquityBasedCompensationLLCUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/EquityBasedCompensationLLCUnitActivityDetails" xlink:type="extended" id="i7f5d603755e64b59b7b781cb732b8b5f_EquityBasedCompensationLLCUnitActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_206ed189-6394-4f9e-9a1d-6fa50668ec0a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_206ed189-6394-4f9e-9a1d-6fa50668ec0a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_36cf6795-ad1e-461a-a1a6-93c2214f6f87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_36cf6795-ad1e-461a-a1a6-93c2214f6f87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_94d49de6-818c-4dc1-adc6-10aec2af1fb2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_94d49de6-818c-4dc1-adc6-10aec2af1fb2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_f2f023d5-9020-43c0-ab06-bfa00010184f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_f2f023d5-9020-43c0-ab06-bfa00010184f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4454e99a-a7d1-4f7b-b70c-18a353acf9c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f900c411-6c3c-4430-8f07-14b1103d124c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4454e99a-a7d1-4f7b-b70c-18a353acf9c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_d2023f89-b6e3-494c-835a-92f56854eedc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_206ed189-6394-4f9e-9a1d-6fa50668ec0a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a5201c7c-1daf-482f-854a-d57f82864ae4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a5201c7c-1daf-482f-854a-d57f82864ae4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e46160d3-f63c-4438-8d46-e78e6639464c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e46160d3-f63c-4438-8d46-e78e6639464c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_8b5ffab8-cb0b-4563-9e05-4d537660df9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_8b5ffab8-cb0b-4563-9e05-4d537660df9c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_118b83c6-1193-409f-bed2-d3f7049123b7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_77ced1fc-08a9-4c9b-a663-c41d062c3e72" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_118b83c6-1193-409f-bed2-d3f7049123b7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d6c0f0f6-dcc8-4711-b52c-1c4cf4350431" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_aa43d920-f689-4e2e-8a49-c134e80dd9ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_206ed189-6394-4f9e-9a1d-6fa50668ec0a" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_aa43d920-f689-4e2e-8a49-c134e80dd9ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_aa43d920-f689-4e2e-8a49-c134e80dd9ad" xlink:to="loc_us-gaap_AwardTypeAxis_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_278f35bd-654f-4d18-908c-a659488d2a2d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_52b5b6c6-7d51-49b1-b2bf-ccfdb1e69d16" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_278f35bd-654f-4d18-908c-a659488d2a2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_LLCUnitsMember_4bbd8cfe-3a8c-4ab4-bb63-b48c1d91cbac" xlink:href="brlt-20210930.xsd#brlt_LLCUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_278f35bd-654f-4d18-908c-a659488d2a2d" xlink:to="loc_brlt_LLCUnitsMember_4bbd8cfe-3a8c-4ab4-bb63-b48c1d91cbac" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/IncomeTaxesandTaxReceivableAgreementDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#IncomeTaxesandTaxReceivableAgreementDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/IncomeTaxesandTaxReceivableAgreementDetails" xlink:type="extended" id="i1915027660764cb48a9f6471db5ed4b4_IncomeTaxesandTaxReceivableAgreementDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxContingencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_355eaeda-9f0a-4b98-9826-2be0353eb511" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_355eaeda-9f0a-4b98-9826-2be0353eb511" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_be316108-8b3a-4041-b57e-11d82ea3719c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_be316108-8b3a-4041-b57e-11d82ea3719c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_ebb5de36-ef22-4680-bd69-daed631cb32c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_ebb5de36-ef22-4680-bd69-daed631cb32c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_DeferredIncomeTaxAssetsRelatedToTaxReceivableAgreement_73cb827d-86c9-4a2a-8378-a1036538c498" xlink:href="brlt-20210930.xsd#brlt_DeferredIncomeTaxAssetsRelatedToTaxReceivableAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_brlt_DeferredIncomeTaxAssetsRelatedToTaxReceivableAgreement_73cb827d-86c9-4a2a-8378-a1036538c498" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NoncontrollingInterestNumberOfSharesPurchased_c687df0a-0569-4393-8761-3dad615d7941" xlink:href="brlt-20210930.xsd#brlt_NoncontrollingInterestNumberOfSharesPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_brlt_NoncontrollingInterestNumberOfSharesPurchased_c687df0a-0569-4393-8761-3dad615d7941" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent_9d3cc95b-ddf1-40f8-9c35-0c46ba3db842" xlink:href="brlt-20210930.xsd#brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_brlt_NoncontrollingInterestTaxBenefitDistributionsToNoncontrollingInterestHoldersPercent_9d3cc95b-ddf1-40f8-9c35-0c46ba3db842" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TaxReceivableAgreementLiabilityNoncurrent_3a34d7a4-ada6-4041-8c2f-3aeade97f463" xlink:href="brlt-20210930.xsd#brlt_TaxReceivableAgreementLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_brlt_TaxReceivableAgreementLiabilityNoncurrent_3a34d7a4-ada6-4041-8c2f-3aeade97f463" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_TaxReceivableAgreementRecognitionInAdditionalPaidInCapitalRedemptionOfInterest_b1df34fa-5c80-4149-911c-4763efff5446" xlink:href="brlt-20210930.xsd#brlt_TaxReceivableAgreementRecognitionInAdditionalPaidInCapitalRedemptionOfInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_brlt_TaxReceivableAgreementRecognitionInAdditionalPaidInCapitalRedemptionOfInterest_b1df34fa-5c80-4149-911c-4763efff5446" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_26105330-928a-474d-8526-225a8caadf4e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxContingencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_7aa25ae8-c2b2-47fd-a54b-a2b2b284a8cc" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_26105330-928a-474d-8526-225a8caadf4e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_9a51a4a8-4660-48c0-8411-c63253198063" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_26105330-928a-474d-8526-225a8caadf4e" xlink:to="loc_srt_StatementScenarioAxis_9a51a4a8-4660-48c0-8411-c63253198063" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_9a51a4a8-4660-48c0-8411-c63253198063_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_9a51a4a8-4660-48c0-8411-c63253198063" xlink:to="loc_srt_ScenarioUnspecifiedDomain_9a51a4a8-4660-48c0-8411-c63253198063_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_57578bff-4c19-4894-b4e8-e91786562f40" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_9a51a4a8-4660-48c0-8411-c63253198063" xlink:to="loc_srt_ScenarioUnspecifiedDomain_57578bff-4c19-4894-b4e8-e91786562f40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_e300d547-fbc1-488b-acf1-73a37dcc7efa" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_57578bff-4c19-4894-b4e8-e91786562f40" xlink:to="loc_srt_ScenarioForecastMember_e300d547-fbc1-488b-acf1-73a37dcc7efa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_66411616-d4ea-447a-aaa5-5a9d5f57b7cb" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_26105330-928a-474d-8526-225a8caadf4e" xlink:to="loc_srt_CounterpartyNameAxis_66411616-d4ea-447a-aaa5-5a9d5f57b7cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_66411616-d4ea-447a-aaa5-5a9d5f57b7cb_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_66411616-d4ea-447a-aaa5-5a9d5f57b7cb" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_66411616-d4ea-447a-aaa5-5a9d5f57b7cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f3e2d1d-ba0d-404b-8143-d262c6158ad6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_66411616-d4ea-447a-aaa5-5a9d5f57b7cb" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f3e2d1d-ba0d-404b-8143-d262c6158ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_ContinuingEquityOwnersMember_e56b4bf5-947f-4e78-8d49-79cfc5898fd8" xlink:href="brlt-20210930.xsd#brlt_ContinuingEquityOwnersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f3e2d1d-ba0d-404b-8143-d262c6158ad6" xlink:to="loc_brlt_ContinuingEquityOwnersMember_e56b4bf5-947f-4e78-8d49-79cfc5898fd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_brlt_BrilliantEarthLLCMember_f63da69c-2da0-4932-90e3-c553dbb1833c" xlink:href="brlt-20210930.xsd#brlt_BrilliantEarthLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f3e2d1d-ba0d-404b-8143-d262c6158ad6" xlink:to="loc_brlt_BrilliantEarthLLCMember_f63da69c-2da0-4932-90e3-c553dbb1833c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="i63d6ad9218644447a92d39568e8e2295_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligation_b59696ce-b796-475c-bd0d-7540a7b6ec36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_PurchaseObligation_b59696ce-b796-475c-bd0d-7540a7b6ec36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_1eda701f-1c23-4769-85c9-b6dc2b6f33e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_1eda701f-1c23-4769-85c9-b6dc2b6f33e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_8517e61d-4b46-4c1e-9184-f6dbf2bd5aea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_8517e61d-4b46-4c1e-9184-f6dbf2bd5aea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInSecondYear_d3638386-4391-4aea-b09d-c9f327a79ed4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInSecondYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_PurchaseObligationDueInSecondYear_d3638386-4391-4aea-b09d-c9f327a79ed4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInThirdYear_8a64bda8-4d58-46a9-a6d0-5bbccc05a531" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInThirdYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_PurchaseObligationDueInThirdYear_8a64bda8-4d58-46a9-a6d0-5bbccc05a531" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentAmount_3bf77a32-05ce-44b5-916b-f9e8a47936af" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentAmount_3bf77a32-05ce-44b5-916b-f9e8a47936af" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_71f96eb3-c477-47e8-8f0f-b8def3d79ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_71f96eb3-c477-47e8-8f0f-b8def3d79ee2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized_c64da09f-d4c6-4fc0-80cc-626b9c9cb801" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_DefinedContributionPlanCostRecognized_c64da09f-d4c6-4fc0-80cc-626b9c9cb801" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_96423838-85b4-47e8-818f-b08ad7b2c1fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_6eefb5e4-cf84-4048-b754-b278b20a55fa" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_96423838-85b4-47e8-818f-b08ad7b2c1fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_96423838-85b4-47e8-818f-b08ad7b2c1fd" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_2d201967-2e99-411f-b810-b6dcb81ef655" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_2cb02ec8-156f-43b1-9c56-6bdeb4dc27ad" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_2d201967-2e99-411f-b810-b6dcb81ef655" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalAdditionsMember_fab132f3-c060-45d5-842f-41010bfd6bb7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalAdditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_2d201967-2e99-411f-b810-b6dcb81ef655" xlink:to="loc_us-gaap_CapitalAdditionsMember_fab132f3-c060-45d5-842f-41010bfd6bb7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://brilliantearth.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="brlt-20210930.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://brilliantearth.com/role/SubsequentEventsDetails" xlink:type="extended" id="i1c591fdfec254dff8de784c7104dddbe_SubsequentEventsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_16ce3f9b-791f-4921-8dd2-9333d767d160" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b5871493-c211-4976-9607-999a403d9547" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_16ce3f9b-791f-4921-8dd2-9333d767d160" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b5871493-c211-4976-9607-999a403d9547" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_dc0d9ee2-9b36-40e7-98b9-6867c99c4e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_16ce3f9b-791f-4921-8dd2-9333d767d160" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_dc0d9ee2-9b36-40e7-98b9-6867c99c4e5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_ed47c636-d357-4b26-af2d-65ef2967f4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_16ce3f9b-791f-4921-8dd2-9333d767d160" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_ed47c636-d357-4b26-af2d-65ef2967f4ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_497692a8-06e0-476f-8bd4-ec816a9a18c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_16ce3f9b-791f-4921-8dd2-9333d767d160" xlink:to="loc_us-gaap_SubsequentEventTable_497692a8-06e0-476f-8bd4-ec816a9a18c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_ceb51e06-ae80-43f4-8ba6-10bbd39d07af" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_497692a8-06e0-476f-8bd4-ec816a9a18c6" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_ceb51e06-ae80-43f4-8ba6-10bbd39d07af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ceb51e06-ae80-43f4-8ba6-10bbd39d07af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ceb51e06-ae80-43f4-8ba6-10bbd39d07af" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ceb51e06-ae80-43f4-8ba6-10bbd39d07af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_deff3963-e6a7-4c51-9140-0a48b5e3fc06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ceb51e06-ae80-43f4-8ba6-10bbd39d07af" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_deff3963-e6a7-4c51-9140-0a48b5e3fc06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_d9e2fb3e-c4d9-45d4-9c1f-de6176c70968" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_deff3963-e6a7-4c51-9140-0a48b5e3fc06" xlink:to="loc_us-gaap_SubsequentEventMember_d9e2fb3e-c4d9-45d4-9c1f-de6176c70968" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_734188c3-1ad5-480b-b782-14829d4ab441" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_497692a8-06e0-476f-8bd4-ec816a9a18c6" xlink:to="loc_us-gaap_AwardTypeAxis_734188c3-1ad5-480b-b782-14829d4ab441" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_734188c3-1ad5-480b-b782-14829d4ab441_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_734188c3-1ad5-480b-b782-14829d4ab441" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_734188c3-1ad5-480b-b782-14829d4ab441_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07e87a5d-c2f3-4629-ac23-0508b71f2ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_734188c3-1ad5-480b-b782-14829d4ab441" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07e87a5d-c2f3-4629-ac23-0508b71f2ad7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_864ec756-c395-4584-8bf0-33e05d62358e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07e87a5d-c2f3-4629-ac23-0508b71f2ad7" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_864ec756-c395-4584-8bf0-33e05d62358e" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
