Miss leading to defeat mainly for French (6)
I believe the answer is:
gallic
'french' is the definition.
(I've seen this before)
'miss leading to defeat mainly' is the wordplay.
'miss' becomes 'gal' (synonyms).
'leading to' is a charade indicator (letters next to each other) (some letters go before or lead others).
'defeat' becomes 'lick'.
'mainly' means to remove the last letter.
'lick' with its last letter taken off is 'lic'.
'gal'+'lic'='GALLIC'
'for' is the link.
(Other definitions for gallic that I've seen before include "Typically French or of France" , "Characteristic of the French" , "Of the French/France" , "Pertaining to France" , "Like certain wars" .)