A cocktail of gin and vermouth (7)
I believe the answer is:
martini
'a cocktail of gin and vermouth' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for martini that I've seen before include "Cocktail of gin and dry vermouth" , "Cocktail made with gin or vodka and vermouth" , "obtained from a bottle" , "Italian drink" , "rifle" .)