/ Dictionary / Index S semis: Meaning and Definition of Find definitions for: se•mis Pronunciation: (sā'mis, sē'-), [key] — n. a copper coin of ancient Rome, the half part of an as. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: semis (Thesaurus) semiround semiserious Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language