It would be better if the question was more specific but I’ll try to answer it as much as I can.
A religious heretic has many other terms. One of the most common would be heathen. This term is commonly used in books. Other synonyms would be dissenter, noncomformist, apostate, freethinker, iconoclast, agnostic, atheist, nonbeliever, unbeliever, idolator, idolatress, pagan and paynim. By definition, a heretic is a person believing in or practicing religious heresy.
I really hope this could help.