"Thinkbox." "Frisking the whiskers." "Buy a woof (wolf) ticket." That's slang for brain, jazz musicians warming up and calling someone's bluff -- just three of hundreds of entries from four centuries of slang compiled in "Juba to Jive: A Dictionary of African-American Slang." Clarence Major, a UC Davis English professor, assembled the dictionary, reprinted in an expanded edition this year, to show the evolution of slang in the African American community. Four categories of slang are represented, including early Southern-rural slang with roots in slavery, sinner-man/black musician slang between 1900 and 1960, and street culture and working-class slang. "Not all black speech is 'street' speech," says Major. He describes slang as a private language, "with its own center of gravity, integrity and shape." And African American slang is "the classic example of a secret tongue. Since the days of slavery, this secrecy has served as a form of cultural self-defense against exploitation and oppression."