IGNORAMUS, n. A person unacquainted with certain kinds of knowledge familiar to yourself, and having certain other kinds that you know nothing about.

Ambrose Bierce (1842-1914?) American writer and journalist

“Ignoramus,” The Cynic’s Word Book (1906)
    (Source)

Included in The Devil's Dictionary (1911). Originally published in the "Devil's Dictionary" column in the San Francisco Wasp (1885-08-29).