Result - the French get cunning for all eternity (9)
I believe the answer is:
endlessly
'for all eternity' is the definition.
I can't tell whether this defines the answer.
'result the french get cunning' is the wordplay.
I cannot quite understand how this works, but
'result' could be 'end' (I've seen this in another clue) and 'end' is found in the answer.
'cunning' could be 'sly' (synonyms) and 'sly' is located in the answer.
'the french' could be 'les' (plural form of 'the' in French) and 'les' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for endlessly that I've seen before include "Limitlessly" , "Ad infinitum" , "all the time" , "in perpetuity" , "Ceaselessly" .)