/ Dictionary / Index R rational number: Meaning and Definition of Find definitions for: ra'tional num'ber Pronunciation: [key] — Math. Math. a number that can be expressed exactly by a ratio of two integers. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. rationalize rational operation Related Content Daily Word Quiz: lyceum Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language