hippopotamus -
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] 
