uncommon vs uncommonness

uncommon is not a noun while uncommonness is a noun.

Word	Noun	Adjective	Verb	Adverb
uncommon	No	Yes	No	No
uncommonness	Yes	No	No	No

uncommon (noun)	uncommonness (noun)
	extraordinariness as a consequence of being rare and seldom encountered
	extraordinariness as a consequence of being marked by an uncommon or superlative quality

uncommon (adjective)	uncommonness (adjective)
not common or ordinarily encountered; unusually great in amount or remarkable in character or kind
marked by an uncommon quality; especially superlative or extreme of its kind