It’s October! Yay! Time to think up some scary things to etymologize! First up: snakes. Although I’m not scared of them, I know people who are, and supposedly they are one of the things that humans are instinctually afraid of. So let’s see where their names come from!
Snake comes from the Old English snaca and before that the Proto Germanic snakon, which can be traced back to the Proto Indo European word sneg, which means to crawl or a thing that creeps along. The word serpent was also used as a name for the wormy reptiles, and it showed up in the early fourteenth century. It comes from the Old French serpent/sarpent and classical Latin serpentem, which just means snake but also has a verb form, serpere, that means to creep. Serpere can also be traced back to a Proto Indo European word, serp, which means to crawl or creep. So because Proto Indo European had two words for crawl, we now have two words meaning snake. Sure.
And now for actual types of snakes. Cobra showed up in 1802—an actual year! But before that it was the phrase cobra capello, which showed up in the late seventeenth century and comes from the Portuguese cobra de capelo, which literally means hooded snake. Cobra can also be traced to the classical Latin colubra, which means…snake. So because it kind of looked like it had a hood, it was a hooded snake. I guess this means that a “cobra snake” is just a snake snake.
Python showed up in the late sixteenth century, although it wasn’t used as a name for a class of snakes until the early nineteenth century. The word came to us by way of Latin, but it was taken from a Greek myth where the god Apollo killed a serpent named Python. I guess they needed a new snake name and just thought python sounded cool.
Viper first showed up in the early fifteenth century, coming from the Middle French vipere and classical Latin vipera, yet another word for snake. Vipera is actually a contraction of vivipera, a combination of the words vivus (living) and parere (to bear). It’s basically a reference to how some snakes in cooler climates don’t lay eggs but keep them inside the mother’s body so they’re kind of born live rather than hatch later. Most (but not all!) kinds of vipers give birth like that so the name is fairly appropriate.
Tony Jebson’s page on the Origins of Old English