co·ad·ju·tor 
(kō′ə-jtər, kō-ăjə-tər)
(kō′ə-jtər, kō-ăjə-tər)n.
1. A coworker; an assistant.
2. Ecclesiastical A subordinate bishop designated as an assistant and usually as a successor to the bishop of a given diocese.
[Middle English coadjutour, assistant, from Latin coadiūtor : co-, co- + adiūtor, assistant (from adiūtāre, to aid; see ADJUTANT).]