Pope

Pope comes from the Latin word papa, and from Greek pappas, both words for "father". It is an ecclesiastical title reserved since about the 9th century exclusively for the bishop of Rome.

In the 3rd to the 5th century, any bishop and even simple priests were referefd to by this title. The title is still used in the East for the Orthodox patriarch of Alexandria and for Orthodox priests, or in Russian, a-tets.