Quiet as the French, boring (7)
I believe the answer is:
silence
'quiet' is the definition.
(synonyms)
'as the french boring' is the wordplay.
'as' becomes 'since' (both can mean 'because').
'the french' becomes 'le' ('the' in French).
'boring' is an insertion indicator (to bore something can mean to drill into it).
'since' enclosing 'le' is 'SILENCE'.
(Other definitions for silence that I've seen before include "License (anag)" , "There's nothing heard" , "It is golden, they say" , "Quiet" , "No talking" .)