Gasp at French eccentric's baggy trousers (10)

I believe the answer is:

pantaloons

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'baggy trousers' is the definition.
(I've seen this before)

'gasp at french eccentric's' is the wordplay.
'gasp' becomes 'pant' (synonyms).
'at french' becomes 'a' (I am not sure about this - if you are sure you should believe this answer much more).
'eccentric's' becomes 'loon's'.
'pant'+'a'+'loons'='PANTALOONS'

Can you help me to learn more?

(Other definitions for pantaloons that I've seen before include "Women's baggy trousers" , "Baggy trousers gathered at the ankles" .)

I've seen this clue in The Independent.

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