Nobleman or chess piece (6)
I believe the answer is:
knight
I believe this clue is a double definition.
'nobleman' is the first definition.
(I've seen this before)
'chess piece' is the second definition.
(knight is a type of chess piece)
(Other definitions for knight that I've seen before include "'Chessman, the horse's head (6)'" , "Chivalrous warrior of olden times" , "Chess piece shaped like hors's head" , "Heroic champion" , "eg Elton John" .)