Slang. Something we all know. And probably use. “Informal language.” Those words not accepted as proper but not bad. That informal language is in fact usually “characterized by vividness and novelty.”
Mostly, the word hasn’t changed that much…but it’s broadened. And is, in fact, itself nearly impossible to trace the etymology of. Various experts have posited various theories, but none can be proven and said experts can’t seem to agree with each other. It might have Scandinavian roots…or French ones…or something else entirely.
What we know is that its first uses were very specific. In 1756 we have a record of it appearing to mean “the specific vocabulary that thieves use.” By 1801 it was the terminology specific to any particular field. But the definition we know now was only a few years behind, having been firmly established by 1818.
So we might not know where it comes from. But we certainly know where it’s been. 😉 And because I have a strange household, my children will occasionally actually argue about whether a word is slang or “accepted.”

Was “slang” acceptable in your family or school growing up?