Obstinate equine (3)
I believe the answer is:
ass
'obstinate equine' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ass that I've seen before include "slow-witted person" , "Small hoofed animal" , "Horse hybrid" , "Foolish person; animal" , "Silly fellow in passionate state" .)