1.  decisiveness(n = noun.attribute) decision - the trait of resoluteness as evidenced by firmness of character or purpose; "a man of unusual decisiveness"
is a kind of firmness, firmness of purpose, resoluteness, resolution, resolve
Antonym: indecisiveness
Derived form adjective decisive₃

2.  decisiveness(n = noun.attribute) conclusiveness, finality - the quality of being final or definitely settled; "the finality of death"
is a kind of definiteness, determinateness
Derived forms adjective decisive₄, adjective decisive₁, adjective decisive₂