argot n.

"pretentious or insincere talk, ostentatious conventionality in speech," 1709. The earliest use is as a slang word for "the whining speech of beggars asking for alms" (1640s), from the verb in this sense (1560s), from Old North French canter (Old French chanter) "to sing, chant," from Latin cantare, frequentative of canere "to sing" (from PIE root *kan- "to sing").

Century Dictionary notes the ecclesiastical use of cantus in Medieval Latin, and writes, "The word cant may thus have become associated with beggars; but there may have been also an allusion to a perfunctory performance of divine service and hence a hypocritical use of religious phrases." The sense in English expanded after 1680 to mean "the jargon of criminals and vagabonds," and from thence the word was applied contemptuously by any sect or school to the phraseology of its rival.

... Slang is universal, whilst Cant is restricted in usage to certain classes of the community: thieves, vagrom men, and — well, their associates. ... Slang boasts a quasi-respectability denied to Cant, though Cant is frequently more enduring, its use continuing without variation of meaning for many generations. [John S. Farmer, Forewords to "Musa Pedestris," 1896]