/ Dictionary / Index L light quantum: Meaning and Definition of Find definitions for: light' quan'tum Pronunciation: [key] — Physics. Physics. photon. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. lightproof light-rail Related Content Daily Word Quiz: tenacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language