Let us begin by defining �slang.� Webster defines it as �the specialized vocabulary and idioms as of criminals and tramps, the purpose of which was to disguise from outsiders the meaning of what was said.�

With that in mind, let us move on to slang�s current poster child, �junk.�

Yes, junk � as in what one traveler famously warned airport security officers not to touch, as in what Brett Favre is alleged to have texted, as in what�s �in the trunk� of women with voluptuous derrieres.

If these references make you feel like an outsider, well, consider counting your blessings. But for those who know that junk is a euphemism for male genitals and, to a lesser extent, female posteriors, the question remains: Why do they call it junk?

After all, Webster also says junk is �useless or worthless stuff.� Name one man who would make that connection.

So we contacted Grant Barrett, a lexicographer in San Diego and editor of the �The Official Dictionary of Unofficial English.� He also is a vice president of the American Dialect Society, an academic group devoted to the study of English in North America since 1889. In 2004, he wrote a definition for �junk� in �The Double-Tongued Dictionary,� for words �from the fringes of English.�

It turns out the origins of �junk� are murky, �so, as expected, �junk equals genitals� doesn�t yield a lot of concrete answers,� Barrett said. �It�s easy to speculate but impossible to prove any number of theories.�

Still, the study of language often leads down some fascinating byways, so let�s look at the theories.

Barrett said the earliest reference for junk as a body part appears to be 1986, when a writer named Ethan Mordden used the term in a story called �Buddies,� in which one character threatened to drag another �outside and kick your junk in.�

Although the context isn�t perfectly clear, Mordden�s fiction often involved gay culture, which lends the term some credibility, Barrett said. �Much slang does first appear as part of the language of a small in-group, such as homosexuals, and then, through accidents of history or quirks of social dynamics, manages to survive, spread and even thrive,� he said.

Still, almost a decade passed before there was another concrete reference, on a discussion board about wrestling. By the turn of the century (or millennium; read into that what you will), the term was catching on.

�Junk� began popping up in blog posts, song lyrics, magazine articles, even Craigslist. It made network TV dialog in �How I Met Your Mother� and �Parks and Recreation.�

Barrett stopped paying close attention around mid-decade but suspects he could find �zillions more uses of the word since.�

As for �junk in the trunk,� Barrett could find no evidence to show one reference is connected to the other.

In the final analysis, he said junk is a euphemism in the same way �package� or �basket� refers to that particular male body part: �It�s kind of a �placeholder� name.�

But probably not for much longer. The airport encounter with TSA officials became a viral video, which has spawned a spate of pitiable songs posted to YouTube, a line of T-shirts and sweatshirts emblazoned with �Don�t Touch My Junk� and endless punch lines from mainstream comics such as Jay Leno � �Have you heard the TSA�s new slogan? We handle more junk than eBay.�

And that�s how a bit of slang starts to die.