Gaiety, fun (9)
I believe the answer is:
merriment
This clue is a double definition.
'gaiety' is the first definition.
(I know that gaiety can be written as merriment)
'fun' is the second definition.
(I know that fun can be written as merriment)
(Other definitions for merriment that I've seen before include "Jollity" , "Gaiety, laughter, fun" , "Joy" , "laughing maybe" , "Hilarity" .)