frivolity vs fun

frivolity and fun both are nouns.

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

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

Other hyponyms of frivolity include giddiness, silliness, levity, playfulness.

frivolity (noun)	fun (noun)
acting like a clown or buffoon	activities that are enjoyable or amusing
something of little value or significance	violent and excited activity
the trait of being frivolous; not serious or sensible	a disposition to find (or make) causes for amusement
	verbal wit or mockery (often at another's expense but not to be taken seriously)