Coadjutor, n.
Etymology: [L. See Co-, and Aid.]
1. One who aids another; an assistant; a coworker. Craftily outwitting her perjured coadjutor. Sheridan.
2. (R. C. Ch.)
The assistant of a bishop or of a priest holding a benefice.
Shades of meaning
Fernald has no entry of its own for coadjutor; he lists it under accessory, associate, auxiliary.
Where he writes about it:
Colleague is used always in a good sense, associate and coadjutor generally so; ally, assistant, associate, attendant, companion, helper, either in a good or a bad sense; abetter, accessory, accomplice, confederate, almost always in a bad sense. — from accessory