Opening for coins (4)
I believe the answer is:
slot
'opening for coins' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slot that I've seen before include "Scheduled time -- aperture for coins" , "Fit into puzzle" , "Space for coin or programme" , "Narrow opening as in gaming machine" , "Hole for e.g. coin" .)