frum
adj.— «“All of a sudden they decided this side of the town is not for them, they needed to go to the other side, because they’re more frum,” she said, using the Yiddish word for religious.» —“Two neighborhoods reveal Orthodox community’s fault lines” by Amy Klein Jewish Journal (Los Angeles, California) Nov. 10, 2006. (source: Double-Tongued Dictionary)
The word is from the German “fromm,” meaning pious. “Frum” is an adjective for Orthodox Jews. A person who is frum is a “frummie.” I’ve heard the latter mostly in reference to women or to groups, not usually to men. It can be a neutral descriptive term or a mildly disdainful one about a person more religious than oneself.