Source : Webster's Revised Unabridged Dictionary (1913)

Catechist \Cat"e*chist\ (k[a^]t"[-e]*k[i^]st), n. [L.
   catechista, fr. Gr.]
   One who instructs by question and answer, especially in
   religions matters.

Source : WordNet®

catechist
     n : one who instructs catechumens in preparation for baptism