/ Dictionary / Index S surface-active agent: Meaning and Definition of Find definitions for: sur'face-ac•tive a'gent Pronunciation: (sûr'fis-ak"tiv), [key] — Chem. Chem. any substance that when dissolved in water or an aqueous solution reduces its surface tension or the interfacial tension between it and another liquid. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. surface surface boundary layer Related Content Daily Word Quiz: feral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language