A mythological horseman? (7)

I believe the answer is:

centaur

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'horseman?' is the definition.
(half horse, half man)

I don't understand how the rest of the clue works.

(Other definitions for centaur that I've seen before include "Mythological horse-man" , "Mythical semi-equine beast" , "beast seemingly half human" , "Mythical creature with the head of a man and the body of a horse" , "Greek mythical creature" .)

I've seen this clue in The Daily Express.

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