French slang

An argot (English pronunciation: /ˈɑːrɡoʊ/; from French argot [aʁˈɡo] 'slang') is a secret language used by various groups—e.g., schoolmates, outlaws, colleagues, among many others—to prevent outsiders from understanding their conversations. The term argot is also used to refer to the informal specialized vocabulary from a particular field of study, occupation, or hobby, in which sense it overlaps with jargon.

Author Victor Hugo was one of the first to research argot extensively. He describes it in his 1862 novel Les Misérables as the language of the dark; at one point, he says, "What is argot; properly speaking? Argot is the language of misery."

The earliest known record of the term argot in this context was in a 1628 document. The word was probably derived from the contemporary name les argotiers, given to a group of thieves at that time.

...
Wikipedia