Volcano: bet goes up (4)
I believe the answer is:
etna
'volcano' is the definition.
(Etna is an example)
'bet goes up' is the wordplay.
'bet' becomes 'ante' (ante is a kind of bet).
'goes up' shows that the letters should be reversed in order.
'ante' back-to-front is 'ETNA'.
(Other definitions for etna that I've seen before include "hotly-tipped runner" , "It can be scorching" , "Italian smoker" , "Explosive type" , "Neat class of volcano in Sicily" .)