Cathedra /(?)/

Cath·e·dra

Cathedra

n.
  1. The official chair or throne of a bishop, or of any person in high authority.
    The Vatican Council declares that the Pope, is infallible “when he speaks ex cathedra.”
    — Addis & Arnold's Cath. Dict.

Phrases & Compounds

Ex cathedra
in the exercise of one's office; with authority.