In three words, an American island (9)

I believe the answer is:

manhattan

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'island' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for manhattan that I've seen before include "Vermouth and whiskey, with a dash of bitters" , "Cocktail of whiskey and sweet vermouth" , "area of New York City" , "Island of New York - cocktail" , "One of the five boroughs of New York City" .)

I've seen this clue in the Evening Standard.

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