/ Dictionary / Index M mole fraction: Meaning and Definition of Find definitions for: mole' frac"tion Pronunciation: [key] the ratio of the number of moles of a given component of a mixture to the total number of moles of all the components. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. molecule molehill Related Content Daily Word Quiz: abscond Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language