I. noun 1. (chiefly in Roman Catholic contexts) the position or authority of an apostle or a religious leader. 2. a group of apostles or religious leaders. • the male-only apostolate.
3. a form of evangelistic activity or work. • their main apostolates lie in the areas of education or nursing services.
– origin late Middle English: from ecclesiastical Latin apostolatus, from apostulus (see apostle).