Duke ---, jazz musician (9)
I believe the answer is:
ellington
This clue is a double definition.
'duke' is the first definition.
(I've seen this before)
'jazz musician' is the second definition.
(I know that Ellington is a jazz musician)
(Other definitions for ellington that I've seen before include "Duke - (Mood Indigo)" , "Duke (of jazz)" , "Musician" , "One Duke" , "Duke --, twentieth century band leader" .)