adjective
Usage: usually capitalized E&O
: of, relating to, or being the body of Eastern churches in communion with the ecumenical patriarch of Constantinople that includes the churches of the ancient patriarchates of Constantinople, Alexandria, Antioch, and Jerusalem and a number of autocephalous often national churches (as the Greek and Russian Orthodox churches) and that adheres to the Niceno-Constantinopolitan Creed and to a rite having the same liturgies in different languages, Communion under both kinds, an ecclesiastical year including days for Old Testament saints and based on the Julian calendar, and a married parish clergy