Frolic boisterously (4)
I believe the answer is:
romp
'frolic boisterously' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for romp that I've seen before include "Make merry at prom" , "Rough play; easy victory" , "Play boisterously" , "sexy fun" , "Boisterous prank" .)