Union Jack. The etymology of the term Union Jack has never, it is presumed, been explained; for it does not occur in any lexicon or glossary. The word "union" obviously arose from the union of the three kingdoms in one great political power. As an alteration in the banner of St. George occurred in the reign of James I., it may, with great probability, be supposed to have been a corruption of the word "Jacques." Such is the opinion of Sir Harris Nicholas, the eminent antiquary.