uncheerfulness vs disposition

uncheerfulness and disposition both are nouns.

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

uncheerfulness (noun)	disposition (noun)
not conducive to cheer or good spirits	the act or means of getting rid of something
a feeling of dreary or pessimistic sadness	your usual mood
	a natural or acquired habit or characteristic tendency in a person or thing
	an attitude of mind especially one that favors one alternative over others