Opera singer (4)
'opera singer' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for diva that I've seen before include "One who sings" , "Successful lady" , "For example Sutherland" , "Female opera star" , "Long narrow top" .)
(Other definitions for lulu that I've seen before include "Outstanding example of its kind - Alban Berg opera - Scottish pop singer, b. 1948" , "Exceptional thing (colloq.); Berg opera" , "Berg's unfinished opera" , "Attractive girl" , "beauty" .)
'opera singer' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for basso that I've seen before include "Lowest male singing voice (sometimes 'profundo')" , "low voice" , "Singer" , "one's deep in sound" .)