Horse-man of myth (7)
I believe the answer is:
centaur
'horse-man of myth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for centaur that I've seen before include "Mythological horse-man" , "Fabulous beast, half man and half horse" , "Mythical equine creature" , "'Mythical creature, half man, half horse (7)'" , "Mythical horseman!" .)