I guess that's mostly because Latin and Ancient Greek fell out of fashion: https://en.m.wiktionary.org/wiki/catechism https://en.m.wiktionary.org/wiki/catechism

I guess that's mostly because Latin and Ancient Greek fell out of fashion: https://en.m.wiktionary.org/wiki/catechism https://en.m.wiktionary.org/wiki/catechism It definitely is still used a lot in its German form "Katechismus" by obedient Christians and I would expect a similar use in English.