/ Dictionary / Index M Mercast: Meaning and Definition of Find definitions for: Mer•cast Pronunciation: (mûr'kast", -käst"), [key] — n. a broadcasting system used by U.S. agencies to deliver messages to government-operated ships. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mercaptopurine Mercator Related Content Daily Word Quiz: tactful Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language