/ Dictionary / Index B beta decay: Meaning and Definition of Find definitions for: be'ta decay" Pronunciation: [key] — Physics. Physics. a radioactive process in which a beta particle is emitted from the nucleus of an atom, raising the atomic number of the atom by one if the particle is negatively charged, lowering it by one if positively charged. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Beta Crucis Betadine Related Content Daily Word Quiz: eccentric Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language