1. a. Belief in and reverence for a supernatural power or powers regarded as creator and governor of the universe. b. A personal or institutionalized system grounded in such belief and worship. 2. The life or condition of a person in a religious order. 3. A set of beliefs, values, and practices based on the teachings of a spiritual leader. 4. A cause, a principle, or an activity pursued with zeal or conscientious devotion.