Cats may have nine of them, but amphibians lead double lives. Clearly a Hellenic word, amphibian comes from Greek amphibios, a word which correctly translates to "living a double life". This, of course, refers to how the animals live both inside the water and outside of it, but that didn't stop this more metaphorical meaning arising. Amphi-, which means "of both kinds", traces to the Proto-Indo-European word ahmbi, or "round". Bios, which you should recognize from the prefix bio- as meaning "life", comes from the Proto-Indo-European mutt gwihwos ("alive"), from the earlier root gweyh ("live"). Interestingly enough, until zoology was beginning to get standardized at the onset of the nineteenth century, amphibian referred to any animal that spent time in and out of the water, including hippos, dragonflies, and crocodiles!
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
The Etymology Nerd