Being old, will droop (4)

I believe the answer is:

wilt

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'droop' is the definition.
(synonyms)

I don't understand the remainder of the clue.

(Other definitions for wilt that I've seen before include "Lose strength and become limp" , "fade" , "(Of plant) become limp" , "Droop in the heat" , "tire?" .)

I've seen this clue in The Guardian and the Sydney Morning Herald.

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