What is the X in X-mas?
late 14c., "spiritual guide," from Medieval Latin curatus "one responsible for the care (of souls)," from Latin curatus, past participle of curare "to take care of" (see cure (v.)). Church of England sense of "paid deputy priest of a parish" first recorded 1550s.
(from Latin vicarius, "substitute"), an official acting in some special way for a superior, primarily an ecclesiastical title in the Christian Church. In the Roman Empire as reorganized by Emperor Diocletian (reigned 284-305), the vicarius was an important official, and the title remained in use for secular officials in the Middle Ages. In the Roman Catholic Church, "vicar of Christ" became the special designation of the popes starting in the 8th century, and eventually it replaced the older title of "vicar of St. Peter."