A performer in a carnival, often presented as a wild man, who performs grotesquely disgusting acts, such as biting the head off a live chicken or snake.
Hence: Any eccentric or strange person; an oddball; an eccentric.
Hence: A student who is socially inept and a misfit in his class, especially one who is an intellectual; a nerd; a dork. (Informal)
Hence: An intellectually inclined person, especially one who is interested in scientific or technical subjects; as, a group of geeks wearing pocket protectors; originally a deprecatory and contemptuous term, but in the 1990's, with the increase in popularity of computers and the frequency of accumulation of great wealth by computer entrepreneurs, it has come to be used with noticeable frequency by technically competent people to refer to themselves, ironically and sometimes proudly. (Informal)