efficaciousness vs efficacy

efficaciousness and efficacy both are nouns.

Word	Noun	Adjective	Verb	Adverb
efficaciousness	Yes	No	No	No
efficacy	Yes	No	No	No

As nouns, efficaciousness and efficacy are synonyms defined as:

efficaciousness and efficacy: capacity or power to produce a desired effect

efficaciousness (noun)	efficacy (noun)
capacity or power to produce a desired effect	capacity or power to produce a desired effect