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Monastic superiors 
A Prior (or Prioress for nuns) is a monastic superior, usually lower in rank than an Abbot or Abbess. In the Rule of St. Benedict the term prior occurs several times, but does not signify any particular superior; it is indiscriminately applied to any superior, be he Abbot, Provost, Dean, etc. In other old monastic rules the term is used in the same generic sense.
With the Cluniac reform the term Prior received a specific meaning; it supplanted the Provost or Dean (praepositus), spoken of in the Rule of St. Benedict. The example of the Cluniac congregations was gradually followed by all Benedictine monasteries, as well as by the Camaldolese, Vallombrosians, Cistercians, Hirsau congregations, and other offshoots of the Benedictine Order.
Monastic congregations of hermit origin generally do not use the title of abbot for the head of any of their houses, in an effort to avoid the involvement with the world the office of an abbot would entail. As a result, it is not in use for the congregation as a whole. Among them, the equivalent term of Prior General is the one used. This applies, e.g., for the Camaldolese and the Carthusians.
Compound and derived titles 
In the Benedictine Order and its branches, in the Premonstratensian Order, and in the military orders there are three kinds of priors: the claustral prior, the conventual prior, and the obedientiary prior.
The claustral prior (Latin prior claustralis), called dean in a few monasteries, holds the first place after the abbot (or grand-master in military orders), whom he assists in the government of the monastery, functioning effectively as the abbot's second-in-charge. He has no ordinary jurisdiction by virtue of his office, since he performs the duties of his office entirely according to the will and under the direction of the abbot. His jurisdiction is, therefore, a delegated one and extends just as far as the abbot desires, or the constitutions of the congregation prescribe. He is appointed by the abbot, generally after a consultation in chapter with the professed monks of the monastery, and may be removed by him at any time. In many monasteries, especially larger ones, the claustral prior is assisted by a subprior, who holds the third place in the monastery. In former times there were in larger monasteries, besides the prior and the subprior, also a third, fourth and sometimes even a fifth prior. Each of these was called circa (or circator), because it was his duty to make the rounds of the monastery to see whether anything was amiss and whether the brethren were intent on the work allotted to them respectively. He had no authority to correct or punish the brethren, but was to report to the claustral prior whatever he found amiss or contrary to the rules. In the Congregation of Cluny and others of the tenth, eleventh and twelfth centuries there was also a greater prior (prior major) who preceded the claustral prior in dignity and, besides assisting the abbot in the government of the monastery, had some delegated jurisdiction over external dependencies of the abbey. In the high days of Cluny, the abbot was assisted by a coadjutor styled Grand-Prior (Grand-prieur in French).
The conventual prior (Latin prior conventualis) is the independent superior of a monastery that is not an abbey (and which is therefore called a "priory"). In some orders, like the Benedictines, a monastery remains a priory until it is considered stable enough and large enough to the elevated to the rank of an abbey. In other Orders, like the Camaldolese and Carthusians, conventual priors are the norm and there are no abbots. (The superior of the major houses of Camaldolese nuns, however, is called an abbess.)
This title, in its feminine form prioress, is used for monasteries of nuns in the Dominican and Carmelite orders.
An Obedientiary Prior heads a monastery created as a satellite of an abbey. When an abbey becomes overlarge, or when there is need of a monastery in a new area, the abbot may appoint a group of monks under a prior to begin a new foundation, which remains a dependency of the mother abbey until such time as it is large and stable enough to become an independent abbey of its own.
A Prior Provincial is head of an area of certain Orders, notably the Dominicans, who are not cenobitic (monks) but mendicant friars. Among Dominicans, a convent, male or female, may be headed by a conventual prior, the province by a prior provincial, but the head of the whole Order is not called prior general, but Master General. In all these Orders the second superior of a monastery is called subprior and his office is similar to that of the claustral prior in the Benedictine Order.
Other orders 
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Compound and derived titles 
- In some Orders there is only one Grand prior, e.g. in the Portuguese Order of Christ; in other Orders there are several, each in charge of a geographical province called grand priory after him, as in the Order of Malta.
See also 
- This article incorporates text from a publication now in the public domain: Herbermann, Charles, ed. (1913). "Prior". Catholic Encyclopedia. Robert Appleton Company.