Setter's quiet spirit (3)
I believe the answer is:
imp
'spirit' is the definition.
(I have seen 'Evil spirit ' mean 'imp' so perhaps 'spirit' could also mean 'imp')
'setter's quiet' is the wordplay.
'setter's' becomes 'im' (I've seen this in other clues).
'quiet' becomes 'p' (music symbol for 'piano').
'im'+'p'='IMP'
(Other definitions for imp that I've seen before include "old-fashioned graft" , "Small devil or sprite" , "Small mischievous sprite" , "little chap" , "Mischievous monkey" .)