Detail of OED - hippopotamus
See OED entry for Hippopotamus

The word hippopotamus comes from the Late Greek, and is made up of two words, meaning ‘river’ and ‘horse’. But the animal itself comes from Africa. The OED defines the word as an ‘African river-horse...a very large beast with a thick heavy hairless body, large muzzle and tusks, and short legs...’. Many zoo-type animals have names with unusual spellings, often because the English word is sourced from another language – however, the word does not always come from the same country as the beast itself, as in this case.

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