There are two main theories about the origin of this "slang":
* From the Dutch word "slengen", meaning "to throw" This suggests "slang" was used to refer to language that was "thrown about" casually, like a playful object.
* From a similar word meaning "to strike" This implies slang was seen as "hitting" the ear, a rough and unexpected way of speaking.
Regardless of its exact origin, the term "slang" was used to describe informal and unconventional language even in the 16th century. So, in a way, the word "slang" has been describing itself since its inception!