E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ex Cathedra (Latin).
With authority. The Pope, speaking ex cathedra, is said to speak with an infallible voiceto speak as the successor and representative of St. Peter, and in his pontifical character. The words are Latin, and mean from the chairi.e. the throne of the pontiff. The phrase is applied to all dicta uttered by authority, and ironically to self-sufficient, dogmatical assertions.