Betting stake (4)
I believe the answer is:
ante
'betting stake' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ante that I've seen before include "Prefix meaning before" , "Each player's initial contribution to the pot" , "advance payment" , "'Behind, before (4)'" , "Player's stake in poker - a ten? (anag)" .)