The Coquillars, a 16th-century company of French bandits, created “an exquisite language” “that other people cannot understand”:

A crocheteur is someone who picks locks. A vendegeur is a snatcher of bags. A beffleur is a thief who draws fools into the game. An envoyeur is a murderer. A desrocheur is someone who leaves nothing to the person he robs. … A blanc coulon is someone who sleeps with a merchant or someone else and robs him of his money, his clothes and everything he has, and throws it from the window to his companion, who waits below. A baladeur is someone who rushes ahead to speak to a churchman or someone else to whom he wants to offer a fake golden chain or a fraudulent stone. A pipeur is a player of dice and other games in which there are tricks and treachery. … Fustiller is to change the dice. They call the court of any place the marine or the rouhe. They call the sergeant the gaffres. … A simple man who knows nothing of their ways is a sire or a duppe or a blanc. … A bag is a fellouse. … To do a roy David is to open a lock, a door, a coffer, and to close it again. … To bazir someone is to kill him. … Jour is torture. … When one of them says, ‘Estoffe!’ it means that he is asking for his booty from some earnings made somehow from the knowledge of the Shell [their syndicate]. And when he says, ‘Estoffe, ou je faugerey!’ it means that he will betray whoever does not pay his part.

Jean Rabustel, public prosecutor and clerk of the court of the viscountcy of Dijon, wrote in summary, “Every trickery of which they make use has its name in their jargon, and no one could understand it, were he not of their number and compact, or if one of them did not reveal it to another.”

(From Daniel Heller-Roazen, Dark Tongues: The Art of Rogues and Riddlers, 2013.)