millenarianism UK /ˌmɪ.lɪˈnɛə.ɹɪ.əˌnɪz.əm/US /ˌmɪl.əˈnɛɹ.i.ənˌɪz.əm/ noun1 •A belief in a coming religious millennium, especially (Christianity) the belief in a coming thousand-year reign of peace heralded by the Second Coming of Christ; utopianism, belief in a coming era of peace and prosperity.It is hard to say for certain just why this brief but notable shift from passive to active millenarianism should have occurred during the Interregnum. — 1971 formsmillenarianisms