Eastern Church

noun

any of the churches originating in countries formerly part of the Eastern Roman Empire, observing an Eastern rite and adhering to the Niceno-Constantinopolitan Creed; Byzantine Church.
Orthodox Church(def 2).

Origin of Eastern Church

First recorded in 1585–95

British Dictionary definitions for eastern church

Eastern Church

noun

any of the Christian Churches of the former Byzantine Empire
any Church owing allegiance to the Orthodox Church and in communion with the Greek patriarchal see of Constantinople
any Church, including Uniat Churches, having Eastern forms of liturgy and institutions