Cheat quiet imp (5)
I believe the answer is:
scamp
'imp' is the definition.
('scamp' can be a synonym of 'imp')
'cheat quiet' is the wordplay.
'cheat' becomes 'scam' (scam is a kind of cheat).
'quiet' becomes 'p' (music symbol for 'piano').
'scam'+'p'='SCAMP'
(Other definitions for scamp that I've seen before include "little monkey" , "Rogue - perform inadequately" , "A young rascal misbehaving in camps" , "Little Devil" , "Tearaway" .)