Persian is famed as the melodic, courtly language of mediaeval poets such as Omar Khayyam and Hafez, but it is a dictionary of vulgar street slang that is taking Iranian literary circles by storm.
At Tehran's annual book fair, the woman running the stall of the dictionary's publisher Nashr-e Markaz had to explain to a disappointed stream of book buyers that the sixth edition had already sold out.
Much of the slang is the vernacular of "Javads", a wayward breed of young men who drive around Tehran, trying to lure girls into their cars.
Unsurprisingly, many of their racy, often chauvinistic expressions derive from their beloved automobiles.
A "zero kilometre", a reference to a car with no mileage on the clock, is a virgin. "Been in an accident" refers to a girl who has become pregnant.
Girls' backsides, a favourite talking point of hot-blooded Javads, are "hubcaps".
The most popular stall at the fair which opened on Monday was one specialising in books on the giddy social life of the Pahlavis, the royal family deposed in the 1979 Islamic revolution.
"Iran's best-sellers at the moment are all contemporary history," said Ahmad Pirani, who contributed to a book on the private life of the last Shah. His colleague Paris reckoned he knew why: "People want to read about this part of history to know who they are."
A white-turbaned mullah leafed through "Wives of the Shah".
In a country with few entertainment's, Tehran's 11-day book fair is viewed as a fun day out. Fast-food and ice-cream vendors do a brisk trade.
Outside the exhibition rooms, couples exchanged tentative, illicit caresses on the lawns as schoolgirls perched on a wall reading Tintin comics.
STRICT CENSORSHIP: Publishing thresholds have relaxed a touch since liberal President Mohammad Khatami came to power in 1997 but his attempts to push through wide-sweeping social reforms have been thwarted by conservative supervisory bodies.
Iran zealously censors any works criticising the Islamic system. It banned "The Stoning of Soraya M", Freidoune Sahebjam's tale of violent, arbitrary justice in rural Iran.
British novelist Salman Rushdie, sentenced to death by an Iranian fatwa in 1989, is still taboo. An American book on male psychology called "All Men Are Jerks Until Proven Otherwise" has also fallen foul of the censors lately.
Religious and scientific texts dominated the fair's book stacks but young people also snapped up horror novels, US rock lyrics and biographies of England footballer David Beckham.
Islamic publishing houses were also selling new technology: swarms of women in the all-enveloping chador gathered round CD-ROM virtual tours of holy shrines.
"I have come here almost every year," said black-bearded law student Hamid Soleimani, 25. He had bought some books on the early martyrs of Shia Islam.
Elsewhere, a young woman in a green silk headscarf thumbed through a Persian translation of "The Fox", D.H. Lawrence's tale of simmering erotic tensions. Other stands were decked with works by American Jewish actor and director Woody Allen.
Adel, a silver-haired religious bookseller from Tehran's sprawling bazaar, said he was complementing his Korans with the adventures of boy-wizard Harry Potter.
"These J.K.Rowling books are selling pretty well," he said.