French lass left in charge (6)
I believe the answer is:
gallic
'french' is the definition.
(I've seen this before)
'lass left in charge' is the wordplay.
'lass' becomes 'gal' (I've seen this before).
'left' becomes 'l' (common abbreviation).
'in charge' becomes 'ic'.
'gal'+'l'+'ic'='GALLIC'
(Other definitions for gallic that I've seen before include "Typically French or of France" , "Pertaining to France" , "Like certain wars" , "Of the French/France" , "Characteristic of the French" .)