Catholic Encyclopedia (1913)/Apparitor
The official name given to an officer in ecclesiastical courts designated to serve the summons, to arrest a person accused, and, in ecclesiastico-civil procedure, to take possession, physically or formally, of the property in dispute, in order to secure the execution of the judge's sentence, in countries where the ecclesiastical forum, in its substantial integrity, is recognized. He thus acts as constable and sheriff. His guarantee of his delivery of the summons is evidence of the knowledge of the summoned of his obligation to appear, either to stand trial, to give testimony, or to do whatever else may be legally enjoined by the judge; his statement becomes the basis of a charge of contumacy against anyone refusing to obey summons.
R.L. BURTSELL