The word nasty first showed up in English in 1390 as nasti, which translates to "filthy", and that eventually evolved to have a broader meaning of "disgusting" in general. Before that, it's a bit of an etymological mystery. It's commonly thought to be related to Dutch nestig and Swedish neskog, which had the same definition. This would suggest an Old Norse origin, but other theories suggest that it's a shortening of Old French villenastre, meaning "bad" (this would make it a relative of villain), that it's from a Middle Dutch word for "nest", or that it traces to Old High German naz, "wet". In short, we have no consensus. A popular urban legend that we can definitely debunk, however, is that it's named after editorial cartoonist Thomas Nast, who was five centuries too late for that to be a thing.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.