Accept wager but not initially (4)
I believe the answer is:
take
'accept' is the definition.
(to accept is to take possession of)
'wager but not initially' is the wordplay.
'wager' becomes 'stake' (wager in poker).
'but not initially' means to remove the first letter.
'stake' with its first letter taken away is 'TAKE'.
(Other definitions for take that I've seen before include "Steal; subtract" , "receipts" , "Remove; consume" , "scene filmed without interruption" , "Receive willingly" .)