You know what "booze" means, of course, but what if you asked someone in London for a definition -- say, 500 years ago? Lexicographer Jonathon Green will tell you the word is a lot older than you might think. He's spent the last quarter century studying slang, and its history, in the English language. The respected editor of the authoritative Cassell's Dictionary of Slang, Jonathon's written over a dozen books on the subject and has collected a database of over 100,000 slang words. He's now working on a mammoth multi-volume dictionary, due out in 2008, that will cover a half a millennium's worth of words, phrases and figures of speech -- salty and otherwise -- that have seeped into English as slang. We talked to Jonathon about his passion:

VT: First of all, how do you define slang?

Jonathon: It's a counter-language. If someone sets up an established way, we human beings seem to find it necessary to come up with something contrary and oppositional. With language you have Standard English, and you have a counter-language, which is slang.

VT: So how old is slang?

Jonathon: As far as English slang goes, and I think it's true of any language which has a slang, I believe it's been around for almost as long as people have been speaking. That said, the first collection of English slang was made in approximately 1535. It was put together by a man named Robert Copland, who brought out a long poem called "The High Waye to the Spitel House," "Spitel House" meaning a hospital. He had talked to the porter of London's biggest hospital and collected the language of criminal beggars. It was very typical of a kind of book in Europe at the time, called a "Beggar Book." The idea was these wandering criminals had a secret language, known as "cant" (from Latin "cantare", to sing) and sometimes as "Peddlers' French" -- for law-abiding people it was as "foreign" a language as real French. If you could have a translation of this language you'd know what they were up to. A lot of slang-gathering in the next 100 years had this "translation" aspect.

VT: Let's fast-forward to today. Isn't slang changing rapidly? How do you keep up with it?

Jonathon: That's always a problem. Right now the speed of transfer is phenomenally fast. All the lexicographer can do is run very quickly alongside it. You can never "finish" a dictionary, in any case -- even more so with slang than Standard English. That' because slang may have a narrow waterfront, but it's very deep.

VT: What do you mean?

Jonathon: In 1938 the writer J.Y.P. Grieg said the basic ingredients of slang were "sex, money and intoxicating liquor". If you factor in drugs, another kind of intoxicant, of course, not that much has changed. I did a taxonomy of my 100,000 words and found that -- unsurprisingly -- the top themes were crime, punishment, sex, parts of the body and what we do with them, insults, drunkenness, stupidity, being sick and so on. So what I mean by "a narrow waterfront" is that compared to Standard English, slang has very few themes. And they all tend to be concrete; there's very little that's abstract. On the other hand, in Standard English, for example, you have one word for intoxicated by liquor, "drunk." It came out around 1340, and we all know what it means. But slang has 3,000 words that mean "drunk" and new ones keep getting invented. So that's what I mean by it's being very deep.

VT: But don't slang words come and go quickly?

Jonathon: A lot do, but you'd be surprised how much older many slang words are than you might think, and the way that they last. For instance, "crew," meaning a gang, has been used since 1570. "Clink," for a prison, has been around since 1515. And "hot," meaning sexually exciting, also goes back to the 16th century. This stuff is old. The majority of my 100,000 words are still in use in the 21st century. The falling off is much less than you'd expect. Of course, there are ephemera, slang that simply doesn't last. The strictly criminal slang of the 16th and 17th century has undoubtedly vanished. Words like "autem," which means a church, and "autem babbler" for a priest. Words like that have vanished forever.