Abbot is a word derived from the Chaldee abba, 'father,' through the Latinised form abbas. The Chaldee word was adopted by the Christian communities as a form of invocation in prayer (see Gal. iv. 6); but the derivative name, at first used of reverend persons, especially aged monks, was ere long reserved, as a title of dignity, for the head of a monastery or abbey. Until the beginning of the 10th century, the head of every monastery was called abbot; but after the reformation of the order of Benedictines, monasteries arose that were dependent upon the mother-monastery of Cluny and without abbots, being presided over by priors or pro-abbates. Many of the orders founded after the 10th century rejected the title, and called their superior prepositus or prior (as the Carthusians, Dominicans, Carmelites, Augustinians), custos or guardian (as the Franciscans), major or rector. The relation of the abbot to his order on the one hand and to his monks on the other varied greatly in the different orders; the Benedictine abbot was wholly independent, while a supreme council at Clairvaux might interfere in the management of all the Cistercian communities. But the abbot was always entitled and bound to enforce the observance of the rules of his order, to administer the goods of the monastery, and to exact unconditional obedience from his monks. Since the 6th century, at least in the Eastern Church, abbots have generally held clerical orders, but at first, and in the Western Church even down to the 11th century, they were not necessarily priests. By the second Nicene Council (787), abbots were empowered to consecrate monks for the lower sacred orders; but they remained in subordination under their diocesan bishops until the 11th century. As abbeys became wealthy, abbots increased in power and influence; many received episcopal titles; and all were ranked as prelates of the church next to the bishops, and had the right of voting in church-councils. Even abbesses contended for the same honours and privileges, but without success. In the 8th and 9th centuries, abbeys began to be granted by the kings to laymen, as rewards for military service; professedly they were granted only temporarily in commendam. Occasionally an abbey voluntarily elected a powerful noble as its head for the sake of his protection, the titular abbot enjoying the revenues, but interfering little with the management of his abbey. In the 10th century, many of the chief abbeys in Christendom were under lay-abbots (Abbates milites, or Abbacomites), while subordinate deans or priors had the spiritual oversight. The members of the royal household received grants of abbeys as their maintenance, and the king kept the richest for himself. Sometimes convents of nuns were granted to men, and monasteries to women of rank. Gradually it became not unusual for one man, lay or ecclesiastical, to hold two or more abbacies at once; but these and the like abuses were, in a great measure, reformed during the 10th century.
The abbot was usually under the jurisdiction of his diocesan bishop; but there were many cases of exempted abbots, who acknowledged no superior but the pope. They then exercised a quasi-episcopal authority over what was practically their diocese, and enjoyed the right to wear the episcopal insignia—an honour often granted without exemption from the authority of the bishop, but conveying the rank of mitred abbot. In England there were twenty-four mitred abbots, who, however, sat in parliament simply as holding baronies under the crown. On the Continent, not a few abbots had princely titles and privileges, voting in the national councils. The election of an abbot belongs, as a rule, to the chapter or assembly of the monks, and is afterwards confirmed by the pope or by the bishop, according as the monastery is independent or under episcopal jurisdiction. But from early times, the pope claimed the right of conferring many abbacies, and the concordat of 1516 gave a similar privilege to the king of France. Popes as well as princes frequently abused this recognised or usurped power by giving abbacies to members of the secular clergy, who were accordingly not bound by the monastic rules of the community over which they presided (especially in France, see ABBÉ). Such abbots, independent of monastic vows, were secular abbots, while those subject to the rule (regula) of a monastic order were regular abbots. In countries which embraced the Reformation, the possessions of abbeys were mostly confiscated by the crown; but in Hanover, Brunswick, and Württemberg, several monasteries and convents were retained as educational establishments, the heads of which retained the title of abbot or abbess. In the Greek Church, the superiors of convents are called Hegument or Mandrites, and general abbots Archimandrites. Amongst Copts and Syrians, abba is a title given to bishops or patriarchs. The head of the Abyssinian Church is called abbuna ('our father'). See MONACHISM.