Number of the French in uniform (6)
I believe the answer is:
eleven
'number' is the definition.
(eleven is a kind of number)
'the french in uniform' is the wordplay.
'the french' becomes 'le' ('the' in French).
'in' indicates putting letters inside.
'uniform' becomes 'even' (both can mean equal or level).
'le' put inside 'even' is 'ELEVEN'.
'of' acts as a link.
(Other definitions for eleven that I've seen before include "Number on a soccer team" , "Number on a side (6)" , "Late" , "Number in a cricket team" , "Cricketing side" .)