Cathedra \Cath"e*dra\, n. [L., fr. Gr. ? seat. See {Chair}.] The official chair or throne of a bishop, or of any person in high authority. {Ex cathedra} [L., from the chair], in the exercise of one's office; with authority. The Vatican Council declares that the Pope, is infallible ``when he speaks ex cathedra.'' --Addis & Arnold's Cath. Dict.