- Hippopotamus
- ‘From the Greek ἱπποπόταμος (hippopotamos, ιππος hippos meaning “horse” and πόταμος potamus meaning “river”).’
- Walrus
- ‘The most likely origin of the word is the Old Norse hrossvalr, meaning “horse-whale”, which was passed in a juxtaposed form to Dutch and the North-German dialects of the Hanseatic League as walros and Walross.’
(↝via Wikipedia in both cases)