One song rejected for another (4)
I believe the answer is:
aria
'for another' is the definition.
I can't judge whether this definition defines the answer.
'one song rejected' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'song' becomes 'air' (I've seen this in another clue).
'rejected' shows that the letters should be reversed in order.
'air' back-to-front is 'ria'.
'a'+'ria'='ARIA'
(Other definitions for aria that I've seen before include "Elaborate accompanied song for solo voice" , "complex song" , "Operatic number" , "Repeated strain" , "Refrain" .)