catechumen (n.)

"oral instruction, catechism," 1753, from Latinized form of Greek katekhesis "instruction by word of mouth," from katekhein "to instruct orally," originally "to resound" (with sense evolution via "to sound (something) in someone's ear" to "to teach by word of mouth"). From kata "down" (in this case, "thoroughly") + ekhein "to sound, ring," from ekhe "sound," from PIE *(s)wagh- "to resound" (see echo (n.)).