fol ‧ ly /ˈfɒli $ ˈfɑːli/ BrE AmE noun ( plural follies )
[ Date: 1200-1300 ; Language: Old French ; Origin: folie , from fol ; ⇨ ↑ fool 1 ]
1 . [uncountable and countable] formal a very stupid thing to do, especially one that is likely to have serious results:
Somerville bitterly regretted his folly at becoming involved.
it would be folly to do something
It would be sheer folly to reduce spending on health education.
the follies of aristocratic society
2 . [countable] an unusual building that was built in the past as a decoration, not to be used or lived in