equestrian [M17th] Both equestrian and equine [L18th] ‘like a horse’ are from Latin equus ‘horse’, a word that goes right back to the earliest times—unsurprisingly, as horses would have been so important to ancient peoples. Its root was also the source of the Greek equivalent to equus, hippos, which is where we get hippopotamus [LME] or ‘river horse’ from hippos and potamos ‘river’.