Piano tune or two (4)
I believe the answer is:
pair
'two' is the definition.
(pair is a kind of two)
'piano tune' is the wordplay.
'piano' becomes 'p'.
'tune' becomes 'air' (I've seen this before).
'p'+'air'='PAIR'
'or' is the link.
(Other definitions for pair that I've seen before include "Two of a kind, as in cards" , "Couple - wed" , "Cereal used as food" , "Two ducks in one game of cricket" , "players of duet?" .)