A definitor is, in Latin, he who defines. In the Catholic Church, however, this is a title with different specific uses. There are secular definitors, who have a limited amount of oversight over a part of a diocese. There are also definitors in religious orders who generally provide council and assistance to the superiors general and provincial superiors of their order.
In a deanery or vicarate forane, which is a grouping of several neighboring parishes within a diocese, a definitor is either the second (and unique) highest office, immediately below the dean or vicar forane and his deputy, or is the priest in charge of any of a number of even smaller districts within the deanery, called definitio. They oversee the ecclesiastical property and generally assist the dean, under the ordinary authority of the bishop. Alternative titles for this position are chamberlain or treasurer. These diocesan offices are not prescribed by canon law, and can be omitted.
In the Cistercian order, the abbot general is assisted by a council of five definitors, traditionally two French-speaking, one German-speaking, one English-speaking and one Dutch-speaking. In the Order of Franciscan Observantines, the definitor is the second highest office of the congregation, below the procurator general. In the Camaldolese order, definitor may be given as the personal title of an abbot. In the Dominican Order a provincial definitor serves under the provincial superior.
The title definitor general is used in the Discalced Carmelites, the Order of Friars Minor, the Order of Friars Minor Capuchin, the Minor Franciscans, and the Franciscan Reformati. These officers are generally elected by the general chapter of their order for a specified period of time.