Don't you know numbers the French burst into? (2,4)
I believe the answer is:
no less
'don't you know' is the definition.
I can't tell whether this defines the answer.
'numbers the french burst into?' is the wordplay.
'numbers' becomes 'nos' ('no' is an abbreviation for number).
'the french burst' becomes 'les' (I can't explain this - if you can you should believe this answer much more).
'into?' is an insertion indicator.
'nos' placed around 'les' is 'NO LESS'.
Can you help me to learn more?
(Other definitions for no less that I've seen before include "Phrase ironically used to express admiration" , "would you believe!" , "praise, ironically" , "Phrase used to express admiration - lesson (anag)" , "Phrase used to emphasise admiration or surprise" .)