Rabbit on piano? Respect! (5)
I believe the answer is:
prate
'rabbit on' is the definition.
(I've seen this before)
'piano? respect' is the wordplay.
'piano?' becomes 'p' (musical abbreviation).
'respect' becomes 'rate' (rate can mean to respect or esteem).
'p'+'rate'='PRATE'
(Other definitions for prate that I've seen before include "Rabbit on" , "Talk too much" , "Taper (anag.)" , "Tattle, chatter" , "Talk foolishly - blab" .)