Can be said to bow under a climber's weight (5)

I believe the answer is:

bough

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'can' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

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(Other definitions for bough that I've seen before include "Substantial branch of a tree" , "Main branch (of tree)" .)

I've seen this clue in the Evening Standard.

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