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