ex cathedra
/ˌekskəˈθiːdrə/adverb & adjective
- with the full authority of office (especially that of the Pope, implying infallibility as defined in Roman Catholic doctrine)权威性地（的）（尤指教皇的权威, 暗指天主教教义所说的教皇绝无谬误）：
as adv. for an encyclical to be infallible the Pope must speak ex cathedra.要使通谕无懈可击, 罗马教皇讲话必须具有权威性。
词源
Latin, 'from the （teacher's） chair', from ex 'from' and cathedra 'seat' （from Greek kathedra）.