Cover used by an American gangster (4)
I believe the answer is:
hood
I believe this is a double definition.
'cover' is the first definition.
(I know that hood is a type of cover)
'an american gangster' is the second definition.
(I've seen this before)
'used by' acts as a link.
(Other definitions for hood that I've seen before include "Head covering of an American gangster" , "See 8" , "Thomas -, Eng. poet" , "See 5" , "Head covering or American car bonnet" .)