/ Dictionary / Index S semigroup: Meaning and Definition of Find definitions for: sem•i•group Pronunciation: (sem'ē-grp"), [key] — n. Math. an algebraic system closed under an associative binary operation. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. semigloss semih. Related Content Daily Word Quiz: procrastinate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language