The Collaborative International Dictionary of English v.0.48:

Catechumen \Cat"e*chu`men\, n. [L. catechumenus, Gr.
   kathchoy`menos instructed, from kathchei^n. See Catechise.]
   (Eccl.)
   One who is receiving rudimentary instruction in the doctrines
   of Christianity; a neophyte; in the primitive church, one
   officially recognized as a Christian, and admitted to
   instruction preliminary to admission to full membership in
   the church.
   [1913 Webster]

WordNet (r) 3.0 (2006):

catechumen
    n 1: a new convert being taught the principles of Christianity
         by a catechist [syn: catechumen, neophyte]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "catechumen":
   Christian, God-fearing man, abecedarian, accepter, alphabetarian,
   apprentice, articled clerk, baby, beginner, believer, boot,
   brother, church member, churchgoer, churchite, churchman,
   churchwoman, communicant, convert, daily communicant, deb,
   debutant, devotee, devotionalist, disciple, entrant, fanatic,
   fledgling, follower, freshman, good Christian, greenhorn, greeny,
   ignoramus, inductee, infant, initiate, laic, lay brother,
   lay sister, layman, laywoman, learner, neophyte, nestling, new boy,
   newcomer, novice, novitiate, parishioner, pietist, postulant,
   probationer, probationist, proselyte, raw recruit, receiver,
   recruit, religionist, rookie, saint, secular, sister, tenderfoot,
   theist, trainee, truster, tyro, votary, zealot