The Collaborative International Dictionary of English v.0.48:

Coadjutor \Co`ad*ju"tor\, n. [L. See Co-, and Aid.]
   1. One who aids another; an assistant; a coworker.
      [1913 Webster]

            Craftily outwitting her perjured coadjutor.
                                                  --Sheridan.
      [1913 Webster]

   2. (R. C. Ch.) The assistant of a bishop or of a priest
      holding a benefice.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coadjutor
    n 1: an assistant to a bishop

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "coadjutor":
   Grand Penitentiary, Holy Father, abuna, acolyte, adjunct, adjutant,
   agent, aid, aide, aide-de-camp, aider, ally, antipope, archbishop,
   archdeacon, archpriest, assistant, associate, attendant, auxiliary,
   bedfellow, best man, bishop, bishop coadjutor, brother,
   brother-in-arms, canon, cardinal, cardinal bishop, cardinal deacon,
   cardinal priest, chaplain, coadjutant, coadjutress, coadjutrix,
   cohort, colleague, companion, compatriot, compeer, comrade,
   confederate, confrere, consociate, consort, crony, curate, dean,
   deputy, diocesan, ecclesiarch, exarch, executive officer, fellow,
   fellow member, help, helper, helpmate, helpmeet, hierarch,
   high priest, lieutenant, metropolitan, papa, paranymph,
   paraprofessional, patriarch, penitentiary, pontiff, pope,
   prebendary, prelate, primate, rector, rural dean, second, servant,
   sideman, subdean, suffragan, supporting actor,
   supporting instrumentalist, vicar



Bouvier's Law Dictionary, Revised 6th Ed (1856):

COADJUTOR, eccl. law. A fellow helper or assistant; particularly applied to
the assistant of a bishop.