In Christianity the specific names and roles of clergy vary by denomination and there is a wide range of formal and informal clergy positions, including deacons, elders, priests, bishops, preachers, pastors, ministers and the Pope. In Islam, a religious leader is often known formally or informally as an imam, mufti, mullah or ayatollah. In Jewish tradition, a religious leader is often a rabbi (teacher) or hazzan (cantor).
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 Clericus, 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.
Buddhist clergy are often collectively referred to as the Sangha, and consist of various orders of male and female monks (originally called bhikshus and bhikshunis respectively). This diversity of monastic orders and styles was originally one community founded by Gautama Buddha during the 5th century BC living under a common set of rules (called the Vinaya). According to scriptural records, these celibate monks and nuns in the time of the Buddha lived an austere life of meditation, living as wandering beggars for nine months out of the year and remaining in retreat during the rainy season (although such a unified condition of Pre-sectarian Buddhism is questioned by some scholars). However, as Buddhism spread geographically over time - encountering different cultures, responding to new social, political, and physical environments - this single form of Buddhist monasticism diversified. The interaction between Buddhism and Tibetan Bon led to a uniquely Tibetan Buddhism, within which various sects, based upon certain teacher-student lineages arose. Similarly, the interaction between Indian Buddhist monks (particularly of the Southern Madhyamika School) and Chinese Confucian and Taoist monks from c200-c900AD produced the distinctive Ch'an Buddhism. Ch'an, like the Tibetan style, further diversified into various sects based upon the transmission style of certain teachers (one of the most well known being the 'rapid enlightenment' style of Linji Yixuan), as well as in response to particular political developments such as the An Lushan Rebellion and the Buddhist persecutions of Emperor Wuzong. In these ways, manual labour was introduced to a practice where monks originally survived on alms; layers of garments were added where originally a single thin robe sufficed; etc. This adaptation of form and roles of Buddhist monastic practice continued after the transmission to Japan. For example, monks took on administrative functions for the Emperor in particular secular communities (registering births, marriages, deaths), thereby creating Buddhist 'priests'. Again, in response to various historic attempts to suppress Buddhism (most recently during the Meiji Era), the practice of celibacy was relaxed and Japanese monks allowed to marry. This form was then transmitted to Korea, during later Japanese occupation, where celibate and non-celibate monks today exist in the same sects. (Similar patterns can also be observed in Tibet during various historic periods multiple forms of monasticism have co-existed such as "ngagpa" lamas, and times at which celibacy was relaxed). As these varied styles of Buddhist monasticism are transmitted to Western cultures, still more new forms are being created.