It is reputed to have given the world the word “chav”; now Cheltenham Ladies’ College is teaching it to talk teen, thanks to a pupil.

The A-Z of Teen Talk, by 13-year-old Lucy van Amerongen, has been a surprise Christmas bestseller among baffled parents who struggle to understand their offspring.

Teen Talk is a language in which “nang” is cool and “phat-free” isn’t. Middle-aged parents may have caught up with the word “minging” for horrible and “laters” for see you later, but few know why “book” is also cool or the reason a “fudge” is a very stupid person. For those still living in the “antwacky” – as in antique – world, “book” is what predictive text on your mobile phone will come up with when you tap in the word cool. And F, U, D, G and E are not good grades at GCSE.

Lucy came up with the idea for the The A-Z of Teen Talk after her parents complained they could not understand her conversations with her sisters Rosie, 11, and Amii, 23.

To those who wonder whether a girl from a posh school can really speak the language of the streets, she says that her book does not try to translate “gangsta” slang, just the words that ordinary teenagers are likely to use.

She spent a year picking friends’ brains to come up with a list of about 300 words and phrases used by teenagers, but which are generally unintelligible to anyone over the age of 20.

They include the word “chav” for the working classes, which is supposedly derived from Ladies’ College slang for “Cheltenham average”.

Lucy sent the typescript to five publishers and three made her an offer for the book. She received an advance of £1,000 from Ravette, a publisher based in Horsham, West Sussex. The pocket-sized book, which was priced at £4.99, sold more than 3,000 copies in Waterstone’s and W. H. Smith in the run-up to Christmas and there are plans for an undated edition.

Since the book came out Lucy, who only started at the college in September, has been inundated with suggestions for words to include in a second edition. She said: “My favourites are ‘random’ and ‘cringe’ for embarrassment, as in ‘it’s a major cringe’.”

Other less familiar terms such as “cotch down” for sleep, “rago” for OK and “zip” for yob are explained in a manner that any “rent” or “mouldy” (parent) could understand.

Lucy also lists the three golden rules: never make eye contact when talking to a mouldy; always mumble inaudibly to stop them eavesdropping; and include the word “like” at least once in every sentence.

She said: “I hope this will clear up a lot of confusion for other families, and it’s a great feeling to see my name in print. My favourite word has to be ‘vanilla’ for boring or dull, but more and more phrases come up everyday.

“I love languages, and I think some parents don’t give teenagers enough credit for some of the words they use. A lot of them are very creative.”

It was a complaint by her father, Victor, who directs television commercials, that led to the book. He said: “We were on holiday and Lucy was chatting to her sisters and it was like they were talking complete alien gibberish. We couldn’t understand a thing they were saying. That’s when Lucy said she should write a dictionary so we could understand them.

“It’s all a bit fun but I bet it will shed a bit of light on the strange mumbo-jumbo of teenager’s talk for a lot of other parents too. I suspect it has been bought as a Christmas gift for parents as most teenagers are far too cool to be seen dead with a dictionary.”

If there is a slang name for Vicky Tuck, the college’s principal, the school’s marketing secretary was not saying. She said: “It is a marvellous achievement to have a book published at the age of 13.”

Nang vocabulary

Bum Enjoy, as in “He bums his PS2”
Clappin Out of date, clapped out
Da Bomb Great, excellent
Ends Area or estate, as in “what ends are you from?”
Flat roofin’ Overworked, stressed
Gratz Thank you
Hench Tough boy, as in henchman I
nnit Word that turns any sentence into a question
Klingon Younger child, particularly your irritating brother or sister
Ledge A legend, someone who is greatly admired
Nang Cool, excellent, brilliant
Off the hook Cool, appealing, fresh
Phat Really cool, great, awesome
Phat-free Uncool, rubbish; the opposite to phat
Shizzle Someone you worship, as in “she’s a real shiz”
Tin-grin Person who wears braces
Uber Very, totally
Vanilla Boring, dull
Za Abbreviation of pizza: “Let’s grab a za before the movie”
Zep Oik, yob, underclass person

. . . and the East London version

Air Being ignored. As in “If you say that again I’m giving you air”
Brapp Sign of respect
Chung, Choong Attractive

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy