catechism: [16] Etymologically, catechism is ‘teaching by the spoken word’. It is a derivative of catechize [15], which comes ultimately from the Greek verb katēkhein, a compound formed from the prefix katá- ‘thoroughly’ and the verb ēkhein ‘sound, resound’ (related to English echo). Thus originally to ‘catechize’ someone was literally to ‘din’ instruction into them, hence ‘instruct orally’. The word came into English via a later ecclesiastical Greek derivative katēkhízein and Latin catēchīzāre. => echo
