U2 singer (4)
I believe the answer is:
bono
'u2 singer' is the definition.
(Bono is the frontman of U2)
This is the entire clue.
(Other definitions for bono that I've seen before include "U2 frontman" , "U2's main singer and lyricist" , "Pro . . . . publico - for the common good" , "Lead singer of U2" , "U2's star vocalist" .)