monotheism Syllabification: (mon·o·the·ism)Pronunciation: /ˈmänəˌTHēˌizəm/Definition of monotheism noun the doctrine or belief that there is only one God. Derivatives monotheist noun & adjective monotheisticPronunciation: /ˌmänəTHēˈistik/ adjective monotheisticallyPronunciation: /ˌmänəTHēˈistik(ə)lē/ adverb Origin: mid 17th century: from mono- 'one' + Greek theos 'god' + -ismmonotheism in other Oxford dictionaries Definition of monotheism in the British & World English dictionary