/ Dictionary / Index G gamma ray: Meaning and Definition of Find definitions for: gam'ma ray" Pronunciation: [key] — Physics. Physics. a photon of penetrating electromagnetic radiationemitted from an atomic nucleus. a photon emitted by an electron as a result of internal conversion. electromagnetic radiation with wavelengths shorter than approximately one tenth of a nanometer. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. gamma iron gamma-ray astronomy Related Content Daily Word Quiz: procrastinate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language