uncheerfulness vs unhappiness

uncheerfulness and unhappiness both are nouns.

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

As nouns, unhappiness is a hypernym of uncheerfulness; that is, unhappiness is a word with a broader meaning than uncheerfulness:

Other hypernyms of uncheerfulness include sadness.

uncheerfulness (noun)	unhappiness (noun)
not conducive to cheer or good spirits	emotions experienced when not in a state of well-being
a feeling of dreary or pessimistic sadness	state characterized by emotions ranging from mild discontentment to deep grief