IPA: /ˌkætɪˈkɛtɪkəl/
KK: /kætɪˈkɛtɪkəl/
Relating to the instruction or teaching of religious principles, especially in a formal setting.
The church offers catechetical classes for those preparing for confirmation.
Catechetical → It is formed from "catechize" (from Greek "katēkhizō", meaning to instruct orally) and the suffix "-ical" (meaning pertaining to). The word "catechetical" refers to something that pertains to the instruction or teaching of religious principles, especially in a systematic way.
Think of 'instructing orally' ('catechize') about religious teachings, and the '-ical' means it relates to that instruction.