/ Thesaurus / U Synonyms of union jack Find synonyms for: Noun1. Union Jack, Union flag, flagusage: national flag of the United KingdomWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. 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