50 Cent pieces (4)
I believe the answer is:
raps
'50 cent pieces' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for raps that I've seen before include "Knocks sharply" , "Sprechgesang pop hits" , "Cracks" , "'Knocks, on the door say (4)'" .)