foolishness vs fatuity

foolishness and fatuity both are nouns.

Word	Noun	Adjective	Verb	Adverb
foolishness	Yes	No	No	No
fatuity	Yes	No	No	No

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

Other hyponyms of foolishness include indiscretion, injudiciousness, absurdity, fatuousness, silliness, asininity.

foolishness (noun)	fatuity (noun)
a stupid mistake	a ludicrous folly
the trait of acting stupidly or rashly
the quality of being rash and foolish