/ Dictionary / Index U Union Day: Meaning and Definition of Find definitions for: Un'ion Day" Pronunciation: [key] a legal holiday in the Republic of South Africa commemorating the founding of the country on May 31, 1910. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Uniondale unionism Related Content Daily Word Quiz: inutiae Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language