The "Toreador Song," for one (4)
I believe the answer is:
aria
'the toreador song for one' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aria that I've seen before include "Imitative art work" , "Song for solo voice from an oratorio, cantata etc" , "Air in an opera" , "part of opera, maybe" , "Nessun Dorma, for example" .)