1. the quality or state of being foolish; lack of good sense or judgment
2. a foolish act, idea, or practice

Examples

• The foolishness of his decision became clear when he lost all his money.
• She regretted the foolishness of her youth.
• It would be foolishness to drive in this storm.
• His constant foolishness annoyed his coworkers.
• The teacher warned against the foolishness of cheating on exams.
• They laughed at the foolishness of the comedy show.
• Such foolishness could have serious consequences.