Fake coin (4)
I believe the answer is:
slug
'fake coin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slug that I've seen before include "Bullet -- shot of liquor" , "Some whisky perhaps" , "slimy type" , "Shell-less mollusc ? bullet" , "Terrestrial mollusc" .)