Excuse the French gentleman (3,3)
I believe the answer is:
let off
'excuse' is the definition.
(I know that excuse can be written as let off)
'the french gentleman' is the wordplay.
'the french' becomes 'le' ('the' in French).
'gentleman' becomes 'toff' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'le'+'toff'='LET OFF'
Can you help me to learn more?
(Other definitions for let off that I've seen before include "Spare" , "Excuse from doing, or refrain from punishing" , "Allowed to go" , "Chance to escape defeat" , "Cause to explode or excuse from duties" .)