/ Dictionary / Index N number line: Meaning and Definition of Find definitions for: num'ber line" Pronunciation: [key] — Math. Math. a straight line on which there is indicated a one-to-one correspondence between points on the line and the set of real numbers. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. numberless number nine iron Related Content Daily Word Quiz: gregarious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language