Judaist n. : One who believes and practices Judaism.

Example:
Why don't people use the term "Judaist" as much?

Taxonomy
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Defination from the web:
Judaist from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... Judaist. One entry found. Main Entry: Ju·da·ist. Pronunciation: ˈjü-dē-ist, ˈjü-də-, jü-ˈdā- Function: noun. Date: circa 1846 : one that ...