A melody recalled in opera (4)
I believe the answer is:
aria
'in opera' is the definition.
(I've seen this before)
'a melody recalled' is the wordplay.
'melody' becomes 'air' (air can mean a tune or melody).
'recalled' shows that the letters should be reversed in order (to recall can mean to bring something back).
'air' in reverse letter order is 'ria'.
'a'+'ria'='ARIA'
(Other definitions for aria that I've seen before include "Musical performance" , "Repeated strain" , "Operatic number" , "Operatic vocal" , "Elaborate accompanied song for solo voice" .)