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]