Coin aperture (4)
I believe the answer is:
slot
'coin aperture' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slot that I've seen before include "This gaming machine operates by insertion of coin" , "Lots (anag.)" , "Space for coin or programme" , "Opening for coin or TV programme" , "Space for inserting coin" .)