Word Study
cathedra
CIDE DICTIONARY
cathedra, n. [L., fr. Gr. seat. See Chair.].
The official chair or throne of a bishop, or of any person in high authority. [1913 Webster]
"The Vatican Council declares that the Pope, is infallible “when he speaks ex cathedra.”" [1913 Webster]
For further exploring for "cathedra" in Webster Dictionary Online