/ Dictionary / Index D deficient: Meaning and Definition of Find definitions for: de•fi•cient Pronunciation: (di-fish'unt), [key] — adj. lacking some element or characteristic; defective: deficient in taste. insufficient; inadequate: deficient knowledge. —n. a person who is deficient, esp. one who is mentally defective. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: deficient (Thesaurus) deficiency judgment deficient number Related Content Daily Word Quiz: heifer Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language