Touches up the French chief (6)
I believe the answer is:
staple
'chief' is the definition.
(thesaurus)
'touches up the french' is the wordplay.
'touches' becomes 'pats' (pat is a kind of touch).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'the french' becomes 'le'.
'pats' backwards is 'stap'.
'stap'+'le'='STAPLE'
(Other definitions for staple that I've seen before include "important things to eat" , "means of keeping papers together" , "Paper-fastening device" , "Main element" , "Basic commodity for which demand is constant" .)