coadjutor

1. A coworker; an assistant. See synonyms at assistant.
2. An assistant to a bishop, especially one designated to succeed the bishop.

[Middle English coadjutour, assistant, from Latin coadiūtor : co-, co- + adiūtor, assistant (from adiūtāre, to aid; see adjutant).]

noun

A person who holds a position auxiliary to another and assumes some of the superior's responsibilities: adjutant, aide, assistant, auxiliary, coadjutant, deputy, helper, lieutenant, second. See help/harm/harmless.

The noun has one meaning:

Meaning #1: an assistant to a Bishop