It's fun (8)
I believe the answer is:
pleasure
'it's fun' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pleasure that I've seen before include "Urgent entreaty begins gratification" , "Enjoyment, happiness" , "A very desirable feeling" , "A repulse (anag.)" , "amusement" .)