Protestantism UK /ˈpɹɒt.ɪs.tən.tɪ.zəm/US /ˈpɹɑ.tɪs.tən.tɪ.zəm/ noun3 •The Protestant (rather than the Roman Catholic or Orthodox) Christian faith. •The beliefs held by the Protestant churches. •Collectively, the Protestant churches or the Protestants. formsProtestantisms