In 1528, an anonymously published book titled Liber Vagatorum appeared in Germany. Later re-titled in English as the Book of Vagabonds and Beggars, it included a glossary of the mysterious slang that was spoken by the underclass at the time. The preface for this enigmatic book was penned by none other than theologian Martin Luther, who recalled being “cheated and befooled by such tramps and liars more than I wish to confess.” He also spent time underscoring “how mightily the devil rules in this world,” pointing to this slang, which was called “thieves’ cant” (also called beggars’ or rogues’ cant) as evidence.

There are manifold underground jargons among the world languages, but thieves’ cant is notable both for its inscrutable origins and its durability. Many different minority groups have been blamed for inventing it (yes, blamed, not credited), notably the Romani people—the group formerly known as gypsies. English writer Thomas Harman, in his 16th-century pamphlet A Caveat or Warning for Common Cursetors, called its authors “wretched, wyly, wandering vagabonds calling and naming themselves Egyptians, deeply dissembling and long hyding and covering their deep deceitful practices.” Martin Luther, meanwhile, bitterly attributed the invention of thieves’ cants to “the Jews.”

The truth is that no one is clear on who started it. All we know is that forms of thieves’ cant began popping up by the 13th century, in various languages in Europe, and were spoken by the lower class as a slang “to the end that their cozenings, knaveries and villainies might not so easily be perceived and known,” as 17th-century English author Samuel Rid wrote. Thomas Harman claimed that the slang was invented around the 1530s by someone who was “hanged all save the head.” What we do know for sure is that over time the language evolved—some say from Welsh Romani, although this too is disputed. It’s also called “peddler’s French," which might indicate a French connection, but is probably just the English insulting the French. Because the creators of cant are unknown and many of their words (deliberately) obfuscated, the roots of many words largely remain a mystery.

That’s what makes thieves’ cant a perfect example of a cryptolect: It’s a secretive jargon that was created specifically to exclude or confuse a particular group—in this case, the cops. Polari, a language spoken by gay Britons in the mid-20th century, is another example of a cryptolect, as is Boontling, which is still being spoken today in Boonville, California.

We still use some words from thieves' cant, including a few that might ring as solidly 20th-century to our ears. For example, phony, a favorite of Holden Caulfield’s in The Catcher in the Rye (1951), might come from fawney, which can be traced back to 1770 in England. A fawney rig was a common ruse wherein “a fellow drops a brass ring, double gilt, which he picks up before the party meant to be cheated, and to whom he disposes of it for less than its supposed, and ten times more than its real, value.” In this scam, the fawney is the ring, and it probably comes from the Irish word for ring: fáinne. A pratfall, wherein someone falls and lands on their butt, often for comedic effect (or sometimes just in reference to an embarrassing mistake), comes from prat, the cant word for buttocks. Stockings (and now any kind of underwear) are still sometimes called drawers, and a liar or cheat is still called a swindler. Other examples of cant that have survived the ages intact include pigeon (to mean a victim or a sucker), grease (meaning to bribe, as in to grease a palm), and left in the lurch (to be betrayed).

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Other words attributed to cant have relatively obvious origins, such as squeeze, meaning wine or liquor, or peel (to strip). Some have logical meanings once you know their arcane references, for example, myrmidon, which is a cant word for a judge and refers originally to a group of Thessalians who were led by Achilles at the siege of Troy, but later came to mean a hired goon. Meanwhile, other etymologies can only be guessed at, like mishtopper (a coat or petticoat) or Oliver, a nickname for the moon. Maybe you had to be there.

Once cant had been established, plenty of books were written that aimed to decode it. Possibly the most useful of these was written by François Villon. Celebrated today for his sardonic poetry, Villon was an itinerant thief and murderer with a predilection for drunken brawls who spent most of his life getting kicked out of various places in France. However, he also had a Master of Arts degree from the University of Paris and a gift for acrostics. Living and working in the mid-1400s, Villon’s poems were written in the early French-based cant. His 11 Ballades en Jargon shed a tiny bit of light on the code that had baffled the public, almost a century before Martin Luther and his anonymous co-author were writing about being befooled by tramps.

Although it’s been a while since folks were publishing books in cant, it still occasionally pops up in print. Beginning in 1978, Advanced Dungeons & Dragons included a little shout-out to thieves’ cant. If you played as a thief, you could speak thieves’ cant to prevent other players from knowing your plots and plans. (In later editions, thieves became rogues, but players still have the option to speak in cant.) An actual glossary wasn’t included in the AD&D manual—this was just an abstract obfuscation—but they still get props for historical accuracy.

Fortunately for us, there are plenty of resources on cant available today, including the thieves’ cant translator at lingojam and a downloadable online dictionary at the Internet Archive. Although the slang changed heavily over the years and from region to region, here’s a short glossary of selected words and phrases, if you want to pinch a few for your everyday speech. Your friends might not understand you, but that’s kind of the point, isn’t it?

rum: fine, good, valuable
jukrum: license, or permission to operate
lullypriggers: thieves who steal wet clothes off of clotheslines
priggers of prancers: horse thieves
priggers of cacklers: hen thieves
onion: a signet ring or other seal
to ride a horse foaled by an acorn: to be hanged at the gallows
marriage-music: the crying of children
to draw the King's picture: to counterfeit money
zad: a very crooked person
picture frame: the gallows
babe in the wood: a rogue imprisoned in the stock or pillory
abbott’s teeth: the chevaux de frise along the top of the wall around King’s Bench Prison in Southwark, London (once known as “Ellenborough’s teeth”)
progg: victuals
coney-catcher (sometimes conny-catcher): a thief, from coney, a nickname for a rabbit raised for the table, referring to the tameness of one’s victim
billingsgate: profanity, from the London fish market of the same name, known for the crude language heard in its stalls
jobber-nott: a tall, stupid fellow
Irish apricots: potatoes
ace of spades: widow
Pontius Pilate: a pawnbroker
chunk o’ gin: diamond
chunk o’ brandy: ruby
berry wine: sapphire
academy: brothel
fortune teller: judge
frummagemmed: strangled or hanged
kate: lock-picker
mort: woman
oak: rich man
rhino: money
vowel: to write an I.O.U.