Release a French pair (8)
I believe the answer is:
uncouple
'release' is the definition.
(I've seen this before)
'a french pair' is the wordplay.
'a french' becomes 'un' ('a' in French).
'pair' becomes 'couple' (synonyms).
'un'+'couple'='UNCOUPLE'
(Other definitions for uncouple that I've seen before include "Separate (carriage from train)" , "Detach (truck from train)" , "Detach (a railway carriage)" , "Disconnect" , "Release" .)