Horse with a saintly head (5)
I believe the answer is:
steed
'horse' is the definition.
(steed is a kind of horse)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for steed that I've seen before include "Swift horse" , "A mount (poet.)" , "Horse, mount" , "Trusty horse" , "(Poetic) horse" .)