(1) The first and strictly ecclesiastical application of this word is to the seat of the bishop in his episcopal church.
(2) The word was; afterwards transferred to the episcopal see itself. Tertullian (De Praescript. 26) speaks of '"Cathedrae Apostolorum," meaning the specially apostolic succession of the bishops of those sees.
(3) Later, the word became used for the Episcopal Church itself, "principalis cathedra," in Cone. Aquisgr., A.D., 789, can. 40, meaning the cathedral as opposed to other churches in the diocese.