Vegas machine (4)
I believe the answer is:
slot
'vegas machine' 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" , "Opening for coin or TV programme" , "Hole for money" , "Small opening, for a coin say" , "Long narrow aperture" .)