verb: (intransitive) To work as a missionary; to do missionary work.
verb: (transitive) To do missionary work among (a people) or in (a particular place).
verb: (transitive, historical) To teach and to bring under the control of European religion and culture through the mission system, as the Spanish did with Native Americans in their colonies.
verb: (transitive) To make suitable for a military (or intelligence gathering, etc) mission.