/ Dictionary / Index D deficient number: Meaning and Definition of Find definitions for: defi'cient num'ber Pronunciation: [key] — Math. Math. a positive number that is greater than the sum of all positive integers that are submultiples of it, as 10, which is greater than the sum of 1, 2, and 5. Also calledCf. abundant number, perfect number. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. deficient deficit Related Content Daily Word Quiz: abominable Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language