unhappy vs unhappiness

unhappy is not a noun while unhappiness is a noun.

Word	Noun	Adjective	Verb	Adverb
unhappy	No	Yes	No	No
unhappiness	Yes	No	No	No

unhappy (noun)	unhappiness (noun)
	emotions experienced when not in a state of well-being
	state characterized by emotions ranging from mild discontentment to deep grief

unhappy (adjective)	unhappiness (adjective)
experiencing or marked by or causing sadness or sorrow or discontent
generalized feeling of distress
marked by or producing unhappiness
causing discomfort