'Double entendre', says French expert (6)
I believe the answer is:
pundit
'expert' is the definition.
(I've seen this before)
'double entendre says french' is the wordplay.
'double entendre' becomes 'pun' (I've seen this before).
'says french' becomes 'dit' ('says' in French).
'pun'+'dit'='PUNDIT'
(Other definitions for pundit that I've seen before include "Learned authority" , "Maestro" , "Person who is an authority on subject" , "Public expert" , "Talking expert" .)