efficaciousness vs efficacious

efficaciousness is a noun but efficacious is not a noun.

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

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

efficaciousness (adjective)	efficacious (adjective)
	marked by qualities giving the power to produce an intended effect
	producing or capable of producing an intended result or having a striking effect