Initial wager (4)
I believe the answer is:
ante
'initial wager' 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 "Player's stake in poker - a ten? (anag)" , "Money put at risk" , "A neat sort of prefix" , "expected from stake" , "'Behind, before (4)'" .)