/ Dictionary / Index R reagent: Meaning and Definition of Find definitions for: re•a•gent Pronunciation: (rē-ā'junt), [key] — n. Chem. a substance that, because of the reactions it causes, is used in analysis and synthesis. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: reagent (Thesaurus) Reaganomics reagin Related Content Daily Word Quiz: placid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language