Joke quietly before row (5)
I believe the answer is:
prank
'joke' is the definition.
('prank' can be a synonym of 'joke')
'quietly before row' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'before' says to put letters next to each other.
'row' becomes 'rank' (I've seen this before**).
'p'+'rank'='PRANK'
(Other definitions for prank that I've seen before include "Escapade" , "(Amusing) trick" , "High-spirited mischief" , "April fool" , "Jape" .)