/ Dictionary / Index D delta ray: Meaning and Definition of Find definitions for: del'ta ray" Pronunciation: [key] — Physics. Physics. a low-energy electron emitted by a substance after bombardment by higher-energy particles, as alpha particles. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. delta particle delta rhythm Related Content Daily Word Quiz: resilient Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language