folly vs japery

folly and japery both are nouns.

Word	Noun	Adjective	Verb	Adverb
folly	Yes	No	No	No
japery	Yes	No	No	No

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

Other hyponyms of folly include meshugaas, mishegaas, mishegoss, buffoonery, clowning, frivolity, harlequinade, prank.

folly (noun)	japery (noun)
foolish or senseless behavior	acting like a clown or buffoon
a stupid mistake
the trait of acting stupidly or rashly
the quality of being rash and foolish