The word "catechist" is a noun that refers to a person who teaches others about religious beliefs, especially in preparation for baptism. This teaching often uses a specific book called a "catechism," which contains a summary of the principles of the faith.
While "catechist" primarily refers to someone who teaches religious education, it can also be understood in a broader sense as anyone who instructs or educates others in a specific subject. However, this broader usage is less common.
There are no specific idioms or phrasal verbs directly related to "catechist," but you might encounter phrases like "teach the faith" or "prepare for baptism" in discussions about the role of a catechist.