French (6)
'french' is the definition.
(I know that french can be written as Gallic)
This is all the clue.
(Other definitions for gallic that I've seen before include "Characteristic of the French" , "Typically French or of France" , "Of the French/France" , "Like certain wars" , "Pertaining to France" .)
(Other definitions for mar that I've seen before include "Detract from" , "Spanish main?" , "Disfigure" , "Make imperfect" , "Oh dear!" .)
(Other definitions for toast that I've seen before include "'----- of the Town': one receiving the acclaim of one's peers" , "Cook by radiant heat" , "A bit of a bloomer, possibly" , "Breakfast item served in rounds" , "Grill - clinking of glasses" .)