What does "hippopotamus" mean?

Hippopotamus: A large, amphibious, herbivorous mammal (Hippopotamus amphibius), common in the rivers of Africa. It is allied to the hogs, and has a very thick, naked skin, a thick and square head, a very large muzzle, small eyes and ears, thick and heavy body, and short legs. It is supposed to be the behemoth of the Bible. Called also zeekoe, and river horse. A smaller species (H. Liberiencis) inhabits Western Africa.