"Il Trovatore," for one (5)
I believe the answer is:
opera
'il trovatore for one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for opera that I've seen before include "Tosca, for example" , "Die Meistersinger is one" , "eg Peter Grimes" , "Norma, say" , "Musical in which all the words are sung" .)