/ Dictionary / Index R refractive index: Meaning and Definition of Find definitions for: refrac'tive in'dex Pronunciation: [key] — Optics. Optics. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. refractive refractivity Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language