On which to rest the bottom? (3)

I believe the answer is:

bed

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'the bottom?' is the definition.
('bed' can be a synonym of 'bottom')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for bed that I've seen before include "Matrimonial duties" , "For sleep and flowers" , "Divan" , "Piece of furniture" , "Bottom of the sea or river" .)

I've seen this clue in the Evening Standard.

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