efficacy efficacity • efficience · · · Info · Definitions · Synonyms · Antonyms · Characters · · efficacy · · Text Latin · · Script 8 · · Length Definitions · · · (noun) capacity or power to produce a desired effect. Synonyms: efficaciousness. Example: "Concern about the safety and efficacy of the vaccine." · · Noun Definition 1 Synonyms · · · efficaciousness · · Synonym 1 Antonyms · · · inefficacy · · Antonym 0 inefficaciousness · · Antonym 1 Characters · · a latin small letter a U+0061 c latin small letter c U+0063 e latin small letter e U+0065 f latin small letter f U+0066 i latin small letter i U+0069 y latin small letter y U+0079