Quiet set having fun? (4)
I believe the answer is:
play
'fun?' is the definition.
('play' can be a synonym of 'fun')
'quiet set' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'set' becomes 'lay' (laying is a kind of setting**).
'p'+'lay'='PLAY'
'having' is the link.
(Other definitions for play that I've seen before include "Drama; engage in games" , "Slack - performance" , "Uncle's premises" , "Frolic" , "Have fun -- theatrical work" .)