What is the X in X-mas?
1765, from Latin equinus, from equus "horse," from PIE root *ekwo- "horse" (cf. Greek hippos, Old Irish ech, Old English eoh, Gothic aihwa-, Sanskrit açva-, Avestan aspa-, Old Church Slavonic ehu-, all meaning "horse").
equine e·quine (ē'kwīn', ěk'wīn')
Of, relating to, or characteristic of a horse.
Of or belonging to the family Equidae, which includes the horses, asses, and zebras.