mission: 1. a : a ministry commissioned by a religious organization to propagate its faith or carry on humanitarian work     b : assignment to or work in a field of missionary enterprise     c (1) : a mission establishment        (2) : a local church or parish dependent on a larger religious organization for direction or financial support     d plural : organized missionary work     e : a course of sermons and services given to convert the unchurched or quicken Christian faith 2. a body of persons sent to perform a service or carry on an activity: as     a : a group sent to a foreign country to conduct diplomatic or political negotiations     b : a permanent embassy or legation     c : a team of specialists or cultural leaders sent to a foreign country