Use betting at conclusion (5)
I believe the answer is:
spend
'use' is the definition.
(spending is a kind of using)
'betting at conclusion' is the wordplay.
'betting' becomes 'sp'.
'at' means one lot of letters go next to another.
'conclusion' becomes 'end' (something's conclusion is its end).
'sp'+'end'='SPEND'
(Other definitions for spend that I've seen before include "Pay out (money)" , "Pay out or use up" , "amount" , "Use up (one's resources)" , "Pay out (on goods)" .)