union·ist [unionistunionists] BrE [ˈjuːniənɪst] NAmE [ˈjuːniənɪst] noun 1. = ↑trade unionist 2.Union·ista person who believes that Northern Ireland should stay part of the United Kingdom 3.Union·ista supporter of the Union during the Civil War in the US Derived Word: ↑unionism