The Terrible Williamsons called it Cant. I know what cant is and argot and slang and lingo and all that. When a group puts a capital letter on it then it becomes a name that does not necessarily closely reflect the meaning of the uncapitalized word.
Do you recall the last names which most of them share. There is one in particular but I can’t remember it. Williamson is probably one of them but not the most common.
They may call it “The Cant” yet “The Cant” of American Irish and Scottish tinkers is a cant mutually unintelligible with each other. There are multiple dialects calling themselves “The Cant”.