An adder is a type of venomous snake, which is appropriate, because it has a poisoned etymology. Okay, maybe that's melodramatic, but it certainly took a surprising turn. Back in Middle English, the word was addere, and before that, it was naddere. Why the dropping of a consonant? Well, in the olden days, people said "a naddere" so much that it became "an addere," and the shift occurred (this is a process known as rebracketing). In Old English, the word was naeddre, and in Proto-Germanic, it was nadro. By then, the meaning had broadened to "a snake" in general, though, phonemically speaking, we have traveled quite a way from the original term. Further reconstructions take us to the Proto-Indo-European root netre, also "snake", which in turn may be from a word sounding like neh and meaning "to twist", because snakes twist. Apparently, there was a bit of natural selection going on: nadder was also a word, briefly, in the nineteenth century, before it faded into obscurity.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd