Great Schism Syllabification: (Great Schism)Pronunciation: /ˈs(k)izəm/Definition of Great Schism 1the breach between the Eastern and the Western Churches, traditionally dated to 1054 and becoming final in 1472. 2the period 1378–1417, when the Western Church was divided by the creation of antipopes. Great Schism in other Oxford dictionaries Definition of Great Schism in the British & World English dictionary