Gainsbourg's stuff? (5)

I believe the answer is:

serge

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'stuff?' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for serge that I've seen before include "Strong twilled worsted fabric" , "Twilled fabric; name" , "Twilled woollen fabric" , "Stuff" , "Frenchman" .)

I've seen this clue in The Sun.

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