mid-14c., "unintelligible talk, gibberish; chattering, jabbering," from Old French jargon "a chattering" (of birds), also "language, speech," especially "idle talk; thieves' Latin." Ultimately of echoic origin (compare Latin garrire "to chatter," English gargle). Often applied to something the speaker does not understand, hence meaning "mode of speech full of unfamiliar terms" (1650s). Middle English also had it as a verb, jargounen "to chatter" (late 14c.), from French.