| protohippus | (n) Pliocene horse approaching donkeys in size |
| genus protohippus | (n) a genus of Equidae |
| Protohippus | ‖n. [ NL., from Gr. &unr_; first + &unr_; horse. ] (Paleon.) A genus of fossil horses from the Lower Pliocene. They had three toes on each foot, the lateral ones being small. [ 1913 Webster ] |