"The Sweetest Taboo" singer (4)
I believe the answer is:
sade
'the sweetest taboo singer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sade that I've seen before include "Jazz-pop group" , "letter from Israel?" , "The Marquis de .... was renowned for cruelty" , "Marquis de ..., famous for taking pleasure in pain" , "The Marquis de . . . . was noted for cruelty" .)