/ Thesaurus / M Synonyms of mare clausum Find synonyms for: Noun1. mare clausum, waterwayusage: (closed sea) a navigable body of water under the jurisdiction of a single nationWordNet 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