/ Dictionary / Index M molecular beam: Meaning and Definition of Find definitions for: molec'ular beam' Pronunciation: [key] a stream of molecules freed from a substance, usually a salt, by evaporation and then passed through a narrow slit for focusing, for investigating the properties of nuclei, atoms, and molecules. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. molecular astronomy molecular biology Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language