/ Thesaurus / C Synonyms of customs union Find synonyms for: Noun1. customs union, unionusage: an association of nations to promote free trade within the union and set common tariffs for nations that are not membersWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: effervescent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language