Piano tunes as duos (5)
I believe the answer is:
pairs
'duos' is the definition.
('pair' can be a synonym of 'duo')
'piano tunes' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'tunes' becomes 'airs' (air can mean a piece of music).
'p'+'airs'='PAIRS'
'as' acts as a link.
(Other definitions for pairs that I've seen before include "Duos" , "Couples" , "golfing matches" .)