<?xml version="1.0" encoding="utf-8"?>
<!--Generated by DFIN XBRL Instance Document - http://www.dfinsolutions.com/ - Version R3.0 - on 28-April-2023 [10:42:22] {PM}-->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
<roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#PvpAdjustmentsOnly" roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
<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" />
<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" />
<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" />
<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" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" />
<definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly">
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#ecd_AllAdjToCompMember" xlink:label="AllAdjToCompMember" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_AmountOfstockAwardsFromSummaryCompensationMember" xlink:label="AmountOfstockAwardsFromSummaryCompensationMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="AmountOfstockAwardsFromSummaryCompensationMember" order="100" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_FairValueAtYearendOfUnvestedAwardsGrantedDuringTheYearMember" xlink:label="FairValueAtYearendOfUnvestedAwardsGrantedDuringTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="FairValueAtYearendOfUnvestedAwardsGrantedDuringTheYearMember" order="101" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_ChangeInFairValueAtYearendFromPriorYearendOfUnvestedAwardsGrantedInPriorYearsMember" xlink:label="ChangeInFairValueAtYearendFromPriorYearendOfUnvestedAwardsGrantedInPriorYearsMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ChangeInFairValueAtYearendFromPriorYearendOfUnvestedAwardsGrantedInPriorYearsMember" order="102" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_ChangeInFairValueAsOfVestingDateFromPriorYearendOfAwardsGrantedInPriorYearsThatVestedDuringTheYearMember" xlink:label="ChangeInFairValueAsOfVestingDateFromPriorYearendOfAwardsGrantedInPriorYearsThatVestedDuringTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ChangeInFairValueAsOfVestingDateFromPriorYearendOfAwardsGrantedInPriorYearsThatVestedDuringTheYearMember" order="103" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_ForPriorYearendFairValueOfAwardsGrantedInPriorYearsThatForfeitedDuringTheYearMember" xlink:label="ForPriorYearendFairValueOfAwardsGrantedInPriorYearsThatForfeitedDuringTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ForPriorYearendFairValueOfAwardsGrantedInPriorYearsThatForfeitedDuringTheYearMember" order="104" />
<loc xlink:type="locator" xlink:href="bkd-20221231.xsd#bkd_TotalAdjustmentsMember" xlink:label="TotalAdjustmentsMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="TotalAdjustmentsMember" order="105" />
</definitionLink>
</linkbase>
