1. lack of good sense; foolishness
2. a foolish act, idea, or practice
3. a costly ornamental building with no practical purpose
Usage: architectural

Examples

• It would be folly to ignore the weather warnings.
• His decision to quit school was pure folly.
• The war proved to be an expensive folly.
• She realized the folly of her impulsive purchase.
• The garden folly was built in the 18th century.
• Investing all his money in one stock was sheer folly.
• The elaborate folly served only to impress visitors.