Alert auditor, it's been damaged by use! (4)

I believe the answer is:

worn

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'damaged by use' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

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(Other definitions for worn that I've seen before include "Damaged by long use" , "Hackneyed, trite" , "Shabby" , "Sported on the body" , "Threadbare" .)

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

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