Island cocktail (9)
I believe the answer is:
manhattan
I believe this clue is a double definition.
'island' is the first definition.
(I've seen this before)
'cocktail' is the second definition.
(manhattan is a kind of cocktail)
(Other definitions for manhattan that I've seen before include "intoxicating drink" , "Vermouth and whisky cocktail - New York borough" , "One of the five boroughs of New York City" , "NY borough" , "Vermouth and whiskey, with a dash of bitters" .)