(A) hoot – or yell (6)
I believe the answer is:
scream
I believe this is a double definition.
'a hoot' is the first definition.
(both can mean a good time)
'yell' is the second definition.
(I know that scream is a type of yell)
(Other definitions for scream that I've seen before include "Holler" , "A shrill cry of fright" , "Hilarious character" , "Riot" , "noise?" .)