Rocker John (5)
I believe the answer is:
elton
'rocker john' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for elton that I've seen before include "Ben --; -- John" , "..... Jonn (musician)" , "First name of singer/songwriter born Reginald Dwight in 1947" , "Let on he's John, the singer" , ". . . . . John (musician)" .)