Fun at party? (4)
I believe the answer is:
ball
This clue is a double definition.
'fun' is the first definition.
(thesaurus)
'party?' is the second definition.
(ball is a kind of party)
'at' is the link.
(Other definitions for ball that I've seen before include "All-round" , "Spherical object" , "Squash, say" , "form of entertainment" , "Bouncer, say" .)