Gangster's girlfriend (4)
I believe the answer is:
moll
'gangster's girlfriend' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for moll that I've seen before include "Hood's girl" , "Gangster's tart" , "Gangster's girl" , "Gangster's female companion" , "Book by Defoe" .)