Catholic

With the exception of some denominations holding to a doctrine of “the 
Elect,” all Christian churches claim to be “Catholic”—universal, that 
is, for all mankind.
Catholicos, plural Catholicoi, is a title used for the head of certain churches in some Eastern Christian traditions. The title implies autocephaly and in some cases its the title of the head of an autonomous church. The word comes from ancient Greek καθολικός, pl. καθολικοί, derived from καθ' ὅλου (kath'olou, "generally") from κατά (kata, "down") and ὅλος (holos, "whole"), meaning "concerning the whole, universal, general"; it originally designated a financial or civil office in the Roman Empire.[1] The name of the Catholic Church comes from the same word.
Between the 4th and 6th centuries, as the older administrative structure began to crumble, the role of the bishops in the western lands of the Empire enabled those lands and their peoples to maintain a semblance of civilization as the authority of Rome vanished. The senatorial aristocracy, especially in the provinces, continued in many places to serve as sources of local authority to complement the authority assumed by the Church. In Late Antiquity, political power often came to be vested in the spiritual offices of the bishops in each region. This transfer of authority from secular officials to ecclesiastical leaders was natural in that, because of the close integration of the secular and ecclesiastical leadership in the Empire, the areas of ecclesiastical administration always coincided with those of the Roman civil administration.
Therefore, as the Catholic and Eastern Orthodox churches began to define their administrative structures, they relied on the older Roman terminology and methods to describe administrative units and hierarchy, which often caused the division between ecclesiastical and secular authority to disappear. In the Eastern Empire, this became fundamental doctrine: see Caesaropapism and State church of the Roman Empire.
Orthodox