Perform song on piano (4)
I believe the answer is:
play
'perform' is the definition.
(playing is a kind of performing)
'song on piano' is the wordplay.
'song' becomes 'lay' (lay is a kind of song**).
'on' means one lot of letters go next to another.
'piano' becomes 'p'.
'lay' after 'p' is 'PLAY'.
(Other definitions for play that I've seen before include "Make sport" , "Frolic" , "Theatrical production" , "Drama; engage in games" , "Have fun -- theatrical work" .)