Of, relating to, or characteristic of a university union society, esp. the Cambridge Union Society; frequenting or debating at the Union. See union…

U.S. Of, relating to, or designating college fraternities or sororities, esp. those with names composed of Greek letters (cf. sense 2b).

Of or relating to a college fraternity; typical or characteristic of such a fraternity or its members, especially with reference to rowdy behaviour.