Poker buy-in (4)
I believe the answer is:
ante
'poker buy-in' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ante that I've seen before include "Stake; before (Lat.)" , "Advance stake" , "Money put at risk" , "A neat sort of prefix" , "Stake (that may be upped?)" .)