/ Dictionary / Index E efficacious: Meaning and Definition of Find definitions for: ef•fi•ca•cious Pronunciation: (ef"i-kā'shus), [key] — adj. capable of having the desired result or effect; effective as a means, measure, remedy, etc.: The medicine is efficacious in stopping a cough. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: efficacious (Thesaurus) effete efficacity Related Content Daily Word Quiz: endear Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language