Last killer leaving America dry (4)
I believe the answer is:
brut
'dry' is the definition.
(type of wine)
'last killer leaving america' is the wordplay.
'last killer' becomes 'Brutus' (killer of Julius Caesar).
'leaving' is a deletion indicator.
'america' becomes 'US' (United States).
'brutus' with 'us' taken away is 'BRUT'.
(Other definitions for brut that I've seen before include "(Of sparkling wines) very dry" , "Unsweetened; very dry" , "Dry (of champagne)" , "Of champagne, not sweet" , "one type of champagne" .)