/ Dictionary / Index A alpha decay: Meaning and Definition of Find definitions for: al'pha decay" Pronunciation: [key] — Physics. Physics. a radioactive process in which an alpha particle is emitted from the nucleus of an atom, decreasing its atomic number by two. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Alpha Centauri alpha-fetoprotein Related Content Daily Word Quiz: kiln Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language