levity vs humorousness

levity and humorousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
levity	Yes	No	No	No
humorousness	Yes	No	No	No

As nouns, humorousness is a hyponym of levity; that is, humorousness is a word with a more specific, narrower meaning than levity:

Other hyponyms of levity include flippancy, light-mindedness, jocoseness, jocosity, merriness, anecdotalism.

levity (noun)	humorousness (noun)
a manner lacking seriousness	the trait of merry joking
feeling an inappropriate lack of seriousness