One of the Three Tenors (7)
I believe the answer is:
domingo
'one of the three tenors' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for domingo that I've seen before include "Placido ... is popular tenor" , "Placido --, opera singer" , "Placido ......., one of the Three Tenors" , "Santo -, capital of Dominican Republic" .)