The word "Cleric" comes from the ecclesiastical Latin Clericus, for those belonging to the priestly class. In turn, the source of the Latin word is from the Ecclesiastical Greek Klerikos (κληρικός), meaning appertaining to an inheritance, in reference to the fact that the Levitical priests of the Old Testament had no inheritance except the Lord. "Clergy" is from two Old French words, clergié and clergie, which refer to those with learning and derive from Medieval Latin clericatus, from Late Latin clericus (the same word from which "cleric" is derived). "Clerk", which used to mean one ordained to the ministry, also derives from clericus. In the Middle Ages, reading and writing were almost exclusively the domain of the priestly class, and this is the reason for the close relationship of these words. Within Christianity, especially in Eastern Christianity and formerly in Western Roman Catholicism, the term cleric refers to any individual who has been ordained, including deacons, priests, and bishops. In Latin Roman Catholicism, the tonsure was a prerequisite for receiving any of the minor orders or major orders before the tonsure, minor orders, and the subdiaconate were abolished following the Second Vatican Council. Now, the clerical state is tied to reception of the diaconate. Minor Orders are still given in the Eastern Catholic Churches, and those who receive those orders are 'minor clerics.'
The use of the word "Cleric" is also appropriate for Eastern Orthodox minor clergy who are tonsured in order not to trivialize orders such as those of Reader in the Eastern Church, or for those who are tonsured yet have no minor or major orders. It is in this sense that the word entered the Arabic language, most commonly in Lebanon from the French, as kleriki (or, alternatively, cleriki) meaning "seminarian." This is all in keeping with Eastern Orthodox concepts of clergy, which still include those who have not yet received, or do not plan to receive, the diaconate.
A priesthood is a body of priests, shamans, or oracles who have special religious authority or function. The term priest is derived from the Greek presbyter (πρεσβύτερος, presbýteros, elder or senior), but is often used in the sense of sacerdos in particular, i.e., for clergy performing ritual within the sphere of the sacred or numinous communicating with the gods on behalf of the community.