funniness vs fun

funniness and fun both are nouns.

Word	Noun	Adjective	Verb	Adverb
funniness	Yes	No	No	No
fun	Yes	No	No	No

As nouns, fun is a hypernym of funniness; that is, fun is a word with a broader meaning than funniness:

funniness: a comic incident or series of incidents
fun: verbal wit or mockery (often at another's expense but not to be taken seriously)

Other hypernyms of funniness include play, sport.

funniness (noun)	fun (noun)
a comic incident or series of incidents	activities that are enjoyable or amusing
	violent and excited activity
	a disposition to find (or make) causes for amusement
	verbal wit or mockery (often at another's expense but not to be taken seriously)