box spring
US /ˈbɑːks sprɪŋ/
UK /ˈbɑːks sprɪŋ/
1.
a mattress foundation consisting of a sturdy wooden frame covered with cloth and containing springs, designed to support a mattress and absorb shock
:
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The new bed came with a mattress and a matching box spring.
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You need a sturdy box spring to properly support your memory foam mattress.