Pay out pounds for fun (4)
I believe the answer is:
play
'fun' is the definition.
(synonyms)
'pay out pounds' is the wordplay.
'out' is an insertion indicator.
'pounds' becomes 'l' (abbreviation e.g. Lsd - pounds, shillings, pence).
'pay' placed around 'l' is 'PLAY'.
'for' is the link.
(Other definitions for play that I've seen before include "Drama; engage in games" , "Slack - performance" , "Work for actors" , "Stage drama" , "Freedom of movement" .)