Gag, as cracked by the French (7)
I believe the answer is:
silence
'gag' is the definition.
(I know that gag is a more specific form of silence)
'as cracked by the french' is the wordplay.
'as' becomes 'since' (both can mean 'because').
'cracked by' is an insertion indicator (inserted letters go into a gap or crack).
'the french' becomes 'le' ('the' in French).
'since' going around 'le' is 'SILENCE'.
(Other definitions for silence that I've seen before include "may be required in court" , "Period of peace" , "Absence of sound" , "There's nothing heard" , "Hush!" .)