Successful move by the French pair (6)
I believe the answer is:
couple
'pair' is the definition.
(I know that pair can be written as couple)
'successful move by the french' is the wordplay.
'successful move' becomes 'coup' (I can't explain this - if you can you should believe this answer much more).
'by' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'coup'+'le'='COUPLE'
Can you help me to learn more?
(Other definitions for couple that I've seen before include "Pair, duo" , "Pair of attached people" , "The pair to join together" , "Married pair; two forces causing rotation" , "Two of a kind" .)