Frenchman's trousers? (5)

I believe the answer is:

jeans

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'frenchman's trousers?' is the definition.
'jeans' can be an answer for 'trousers?' (denim trousers). I'm unsure of the 'frenchman's' bit.

'frenchman's trousers?' is the wordplay.
'frenchman' becomes 'jean' (I've seen this before).
'trousers?' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'jean'+'s'='JEANS'

Can you help me to learn more?

(Other definitions for jeans that I've seen before include "Strides casually" , "article of clothing" , "Denim trousers" , "Denims" , "Are they worn by girls in Britian" .)

I've seen this clue in The Times.

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