A vicar (/ˈvɪkər/; Latin: vicarius) is a representative, deputy or substitute; anyone acting "in the person of" or agent for a superior (compare "vicarious" in the sense of "at second hand").
Linguistically, vicar is akin with the English prefix "vice", similarly meaning "deputy".
The title appears in a number of Christian ecclesiastical contexts, but also as an administrative title, or title modifier, in the Roman Empire.
In addition, in the Holy Roman Empire a local representative of the emperor, perhaps an archduke, might be styled "vicar".
An imperial vicar (German: Reichsvikar) was a prince charged with administering all or part of the Holy Roman Empire on behalf of the emperor. Later, an imperial vicar was invariably one of two princes charged by the Golden Bull with administering the Holy Roman Empire during an interregnum.
1. Church of England
a. (in Britain) a clergyman appointed to act as priest of a parish from which, formerly, he did not receive tithes but a salary.
b. a clergyman who acts as assistant to or substitute for the rector of a parish at Communion
c. (in the US) a clergyman in charge of a chapel
2. Roman Catholic Church; a bishop or priest representing the pope or the ordinary of a diocese and exercising a limited jurisdiction
3. Church of England a member of a cathedral choir appointed to sing certain parts of the services
(Collins Discovery Encyclopedial
Vicar
(1) In the Late Roman Empire the ruler of an administrative district, or diocese.
(2) In the Orthodox Church an assistant to the eparchial bishop in administering an eparchy.
(3) In the Roman Catholic Church there are general vicars, or assistants to bishops in administering church dioceses, and parish vicars, or assistants to parish priests (cures), who substitute for them when they are ill or absent. There are also apostolic vicars, or papal assistants, most of whom are in remote (missionary) regions. (In 1969 there were 83 apostolic vicars.)