/ Dictionary / Index I inefficacious: Meaning and Definition of Find definitions for: in•ef•fi•ca•cious Pronunciation: (in"ef-i-kā'shus), [key] — adj. not able to produce the desired effect; ineffective. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: inefficacious (Thesaurus) ineffectual inefficacy Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language