Cavort at Prom, possibly (4)
I believe the answer is:
romp
'cavort' is the definition.
(synonyms)
'prom possibly' is the wordplay.
'possibly' is an anagram indicator.
'prom' with letters rearranged gives 'ROMP'.
'at' is the link.
(Other definitions for romp that I've seen before include "Boisterous party" , "Frolic" , "Dance" , "Boisterous prank" , "Play in a lively way, like children" .)