unstableness vs unstable

unstableness is a noun but unstable is not a noun.

Word	Noun	Adjective	Verb	Adverb
unstableness	Yes	No	No	No
unstable	No	Yes	No	No

unstableness (noun)	unstable (noun)
the quality or attribute of being unstable and irresolute

unstableness (adjective)	unstable (adjective)
	lacking stability or fixity or firmness
	subject to change; variable
	suffering from severe mental illness
	disposed to psychological variability
	highly or violently reactive
	affording no ease or reassurance