Italian vermouth (7)
'italian vermouth' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for martini that I've seen before include "Sienese painter" , "Cocktail of gin and dry vermouth" , "Gin or vodka with dry vermouth" , "alcoholic drink" , "Cocktail made with gin or vodka and vermouth" .)
(Another definition for cinzano that I've seen is " Brand of Italian vermouth".)