One of my friends recently asked me if slang is a portmanteau of "short language". While this makes a funny pun, those kinds of blendings are rarer and tend to be more modern. While we're uncertain about its exact origin, the word slang began showing up in London in the middle of the eighteenth century and, ironically enough, seems to have originally been a slang term referring to Thieves' Cant. Beyond that, the best theory that I found is that slang comes from a Germanic word meaning "sling", on the notion of words being casually slung around. It might also be from a dialect in Northern England, where it meant "turf", and got applied to one's own vernacular just as it was used for one's own property. Finally, it's similar to the Norwegian noun slengenamn, meaning "nickname", but a connection doesn't seem to make chronological and geographical sense.
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.