It's a pleasure! (3)
I believe the answer is:
fun
'it's a pleasure' is the definition.
(fun is enjoyment or pleasure)
This is the entire clue.
(Other definitions for fun that I've seen before include "Light-hearted amusement, jollity" , "Playful amusement" , "Light-hearted pleasure" , "Jollification" , "Entertaining" .)