Wordnet 3.0
ADVERB (1)
1.
with the full authority of the office;
- Example: "the pope must speak ex cathedra for an encyclical to be infallible"
The Collaborative International Dictionary of English v.0.48:
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.
[1913 Webster]
Ex cathedra [L., from the chair], in the exercise of one's
office; with authority.
[1913 Webster]
The Vatican Council declares that the Pope, is
infallible "when he speaks ex cathedra." --Addis &
Arnold's Cath.
Dict.
[1913 Webster]
WordNet (r) 3.0 (2006):
ex cathedra
adv 1: with the full authority of the office; "the pope must
speak ex cathedra for an encyclical to be infallible"