Mythical man-horse (7)
I believe the answer is:
centaur
'mythical man-horse' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for centaur that I've seen before include "Mythological man-horse" , "Mythical hybrid" , "Mythical creature, half-man, half-horse" , "Mythical horseman!" , "Mythological horse-man" .)