decisiveness vs conclusive

decisiveness is a noun but conclusive is not a noun.

Word	Noun	Adjective	Verb	Adverb
decisiveness	Yes	No	No	No
conclusive	No	Yes	No	No

decisiveness (noun)	conclusive (noun)
the trait of resoluteness as evidenced by firmness of character or purpose
the quality of being final or definitely settled

decisiveness (adjective)	conclusive (adjective)
	forming an end or termination; especially putting an end to doubt or question