Logic helping the French to accept answer (9)
I believe the answer is:
rationale
'logic' is the definition.
(I've seen this before)
'helping the french to accept answer' is the wordplay.
'helping' becomes 'ration' (a ration is a serving or helping).
'the french' becomes 'le' ('the' in French).
'to accept' means one lot of letters goes inside another.
'answer' becomes 'a' (abbreviation eg in Q and A).
'ration'+'le'='rationle'
'rationle' going around 'a' is 'RATIONALE'.
(Other definitions for rationale that I've seen before include "Logical reasons (for action)" , "Good reason" , "Underlying principle" , "grounds?" , "The logical basis of some thing or action" .)