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