Equine hybrid (4)
I believe the answer is:
mule
'equine hybrid' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mule that I've seen before include "Donkey-horse hybrid" , "Illegal drugs courier" , "Sterile offspring of donkey and horse" , "Proverbially stubborn beast" , "Obstinate creature" .)