unionist Syllabification: (un·ion·ist)Pronunciation: /ˈyo͞onyənist/Definition of unionist noun 1a member of a labor union. an advocate or supporter of labor unions. 2 (Unionist) a person who opposed secession during the Civil War. a person in Northern Ireland, especially a member of a political party, supporting or advocating union with Great Britain. Derivatives unionismPronunciation: /-ˌnizəm/ noun unionisticPronunciation: /ˌyo͞onyəˈnistik/ adjective unionist in other Oxford dictionaries Definition of unionist in the British & World English dictionary