n. (pl. hippopotamuses or hippopotami) 1 a large thick-skinned four-legged mammal, Hippopotamus amphibius, native to Africa, inhabiting rivers, lakes, etc. 2 (in full pigmy hippopotamus) a smaller related mammal, Choeropsis liberiensis, native to Africa, inhabiting forests and swamps.
[ ME f. L f. Gk hippopotamos f. hippos horse + potamos river ]