Bet volcano is elevated (4)
I believe the answer is:
ante
'bet' is the definition.
(ante is a kind of bet)
'volcano is elevated' is the wordplay.
'volcano' becomes 'etna' (Etna is an example).
'is elevated' says the letters should be written in reverse.
'etna' backwards is 'ANTE'.
(Other definitions for ante that I've seen before include "not post" , "'Behind, before (4)'" , "early payment" , "Initial bet" , "Preposition meaning before" .)