Quick profit involving cocaine (4)
I believe the answer is:
pacy
'quick' is the definition.
'profit involving cocaine' is the wordplay.
'profit' becomes 'pay' (I've seen this before).
'involving' means one lot of letters goes inside another.
'cocaine' becomes 'C' (drugs abbreviation).
'pay' going around 'c' is 'PACY'.
(Other definitions for pacy that I've seen before include "Showing good turn of speed" , "Fleet" , "Fast" , "nippy" .)