/ ˈfɒli; NAmE ˈfɑːli/ noun ( pl. -ies )
1.
[ U , C ] folly (to do sth) a lack of good judgement; the fact of doing sth stupid; an activity or idea that shows a lack of judgement
SYN stupidity :
an act of sheer folly
Giving up a secure job seems to be the height of folly.
It would be folly to turn the offer down.
the follies of youth
2.
[ C ] a building that has no practical purpose but was built in the past for decoration, often in the garden of a large country house
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WORD ORIGIN
Middle English : from Old French folie madness, in modern French also delight, favourite dwelling (compare with sense 2), from fol fool, foolish.