uninterestingness vs uninteresting

uninterestingness is a noun but uninteresting is not a noun.

Word	Noun	Adjective	Verb	Adverb
uninterestingness	Yes	No	No	No
uninteresting	No	Yes	No	No

uninterestingness (noun)	uninteresting (noun)
inability to capture or hold one's interest

uninterestingness (adjective)	uninteresting (adjective)
	arousing no interest or attention or curiosity or excitement
	characteristic or suggestive of an institution especially in being uniform or dull or unimaginative