/ Dictionary / Index M Mare Tyrrhenum: Meaning and Definition of Find definitions for: Ma're Tyr•rhe'num Pronunciation: (ti-rē'num), [key] (Tyrrhenian Sea) an area in the southern hemisphere of Mars, appearing as a dark region when viewed telescopically from the earth. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Mare Tranquillitatis Mare Undarum Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language