frivolity vs silliness

frivolity and silliness both are nouns.

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

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

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

frivolity (noun)	silliness (noun)
acting like a clown or buffoon	a ludicrous folly
something of little value or significance	an impulsive scatterbrained manner
the trait of being frivolous; not serious or sensible