/ Dictionary / Index B big bang theory: Meaning and Definition of Find definitions for: big' bang' the"ory Pronunciation: [key] — Astron. Astron. a theory that deduces a cataclysmic birth of the universefrom the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics. Also calledCf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Big Band music big beat Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language