Definition from Wiktionary, the free dictionary
- The religious belief that God is a single Person.
the religious belief that God is a single person
Proper noun 
- (beginning in 1565) The religion of the Unitarian Church of Transylvania
- (beginning in 1774) The religion of the General Assembly of Unitarian and Free Christian Churches
- (1825-1961) The religion of the American Unitarian Association
- (beginning in 1961) Short for the religion known as Unitarian Universalism