1The Christian religion; Christianity.
Frequently contrasted with other nouns referring to religions, beliefs, or ways of life, such as Judaism, Heathenism, etc.,.
2US (usually depreciative). A movement which advocates greater influence of conservative Christian beliefs in politics and society; Christian fundamentalism.
Christianism/ˈkrɪstʃ(ə)nɪz(ə)m/ /ˈkrɪstjənɪz(ə)m/ /ˈkrɪstɪənɪz(ə)m/
Mid 16th century. Originally from post-classical Latin christianismus the Christian religion (3rd century), Christendom from Hellenistic Greek χριστιανισμός Christianity from χριστιανός + -ισμός.