King murdered by Macbeth (6)
I believe the answer is:
duncan
'king murdered by macbeth' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for duncan that I've seen before include "Scottish king" , "innovative dancer" , "Isadora ..., pioneer of modern dance" , "King murdered by ambitious Macbeth" , "Man's name" .)