efficacy vs efficaciousness

efficacy and efficaciousness both are nouns.

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

As nouns, efficacy and efficaciousness are synonyms defined as:

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

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