Cotton-based fabric which is twilled, unlike duck (5)

I believe the answer is:

denim

(Other definitions for denim that I've seen before include "Hard-wearing material seen in jeans" , "Fabric used for jeans" , "Coarse durable twill-weave cotton fabric" , "Durable material" , "Hard-wearing cotton fabric" .)

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

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