Post a bet (5)
I believe the answer is:
stake
I believe this is a double definition.
'post' is the first definition.
(I know that post can be written as stake)
'a bet' is the second definition.
(I know that bet can be written as stake)
(Other definitions for stake that I've seen before include "Money placed as bet" , "Amount gambled" , "Post; money for bet" , "Wager; post" , "Share (in a business); post" .)