Why is the ninth month called September?
1860, from French argot (17c.) "the jargon of Paris rogues and thieves," earlier "the company of beggars," from Middle French argot, "group of beggars," origin unknown. Gamillscheg suggests a connection to Old French argoter "to cut off the stubs left in pruning," with a connecting sense of "to get a grip on." The best English equivalent is perhaps cant. The German equivalent is Rotwelsch, literally "Red Welsh," but the first element may be connected with Middle High German rot "beggar." Earlier in English was pedlar's French (1520s) "language of thieves and vagabonds."