Feature trousers, one third off (4)

I believe the answer is:

chin

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'feature' is the definition.
(facial feature)

I can't explain the rest of the clue.

(Other definitions for chin that I've seen before include "What's repeatedly required for a toast" , "Part of the face (on which one may have to take it?)" , "Possible double feature?" , "Bottom part of jaw" , "Point of the jaw" .)

I've seen this clue in The Independent.

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