Soprano's solo (4)
I believe the answer is:
aria
'soprano's 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 "Musical performance" , "Operatic song" , "Song from an opera (4)" , "Song for solo voice from an oratorio, cantata etc" , "Summertime perhaps" .)