1The hippopotamus, Hippopotamus amphibius. Now rare.

2Newfoundland. A pile or stack of split and salted whole cod, rinsed and arranged in layers to drain before drying. Also occasionally as mass noun. Sometimes attributive, especially as "waterhorse fish".

3Mythology. In Scotland and northern England: a spirit, usually taking the form of a horse, said to haunt lakes and other bodies of water.