Bet animal is cut in half (4)
I believe the answer is:
ante
'bet' is the definition.
(ante is a kind of bet)
'animal is cut in half' is the wordplay.
'animal' becomes 'ant' (ant is a kind of animal).
'is' becomes 'be'.
'cut in half' suggests halving the letters.
'be' halved is 'e'.
'ant'+'e'='ANTE'
(Other definitions for ante that I've seen before include "Each player's initial contribution to the pot" , "Money for poker" , "Player's stake in poker - a ten? (anag)" , "Initial stake in a poker game" , "Stake, bet" .)