Operatic solo (4)
I believe the answer is:
aria
'operatic solo' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aria that I've seen before include "Nessun Dorma, for example" , "Operatic part" , "Song for solo voice from an oratorio, cantata etc" , "Operatic song" , "selection of opera" .)