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).