Little width in very informal trousers (5)

I believe the answer is:

trews

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'trousers' is the definition.
(trews is a kind of trousers)

I don't understand how the rest of the clue works.

(Other definitions for trews that I've seen before include "Item of clothing" , "nether garments" , "close-fitting garments" , "Close-fitting tartan trousers" , "Garment" .)

I've seen this clue in The Times and The Sunday Times.

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