What term describes any Western Christian who is not an adherent to the Roman Catholic faith?

The term that describes any Western Christian who is not an adherent to the Roman Catholic faith is "Protestant." This designation emerged during the Reformation in the 16th century when various groups broke away from the Roman Catholic Church to form their own denominations based on differing beliefs regarding theology, church governance, and practices.

Protestants can include a variety of denominations such as Lutherans, Baptists, Methodists, and Anglicans, among others, and they share essential characteristics such as the emphasis on the authority of Scripture and justification by faith. This term does not encompass Orthodox Christians, who belong to Eastern Christian traditions, nor does it describe Roman Catholics themselves, who remain part of the Catholic tradition. The term "Orthodox Jew" pertains specifically to a branch of Judaism, distinguishing it from Christian classifications. Thus, "Protestant" accurately captures the identity of those Western Christians outside of the Roman Catholic faith.