Horse with a saintly head (5)

I believe the answer is:

steed

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'horse' is the definition.
(steed is a kind of horse)

I don't understand the remainder of the clue.

(Other definitions for steed that I've seen before include "Swift horse" , "A mount (poet.)" , "Horse, mount" , "Trusty horse" , "(Poetic) horse" .)

I've seen this clue in the Evening Standard.

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