/ Dictionary / Index D deficiency: Meaning and Definition of Find definitions for: de•fi•cien•cy Pronunciation: (di-fish'un-sē), [key] — pl. -cies. the state of being deficient; lack; incompleteness; insufficiency. the amount lacked; a deficit. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: deficiency (Thesaurus) deficience deficiency account Related Content Daily Word Quiz: eureka Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language