Crossword Genius

If its end became soft, would it go limp? (4)

Ross

I believe the answer is:

limb

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'limp?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I can't explain the remainder of the clue.

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(Other definitions for limb that I've seen before include "Large tree branch" , "as part of plane, say" , "Tentacle" , "Wing, perhaps" , "Jointed appendage" .)

I've seen this clue in the Evening Standard.
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