Stunning success, the French pair (6)
I believe the answer is:
couple
'pair' is the definition.
(I know that couple is a action)
'stunning success the french' is the wordplay.
'stunning success' becomes 'coup' (I've seen this in another clue).
'the french' becomes 'le' ('the' in French).
'coup'+'le'='COUPLE'
(Other definitions for couple that I've seen before include "item" , "Twosome" , "Two - join up" , "Pair, duo" , "Duo, brace" .)