/ Dictionary / Index D Descartes' law: Meaning and Definition of Find definitions for: Descartes'' law' Pronunciation: [key] — Optics. Optics. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Descartes descend Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language