Ruby of "American Gangster” (3)
I believe the answer is:
dee
'ruby of american gangster' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dee that I've seen before include "Scottish river" , "River at Chester" , "John ---, Elizabethan mage" , "Chester's river" , "Balmoral's river" .)