Lacking good sense or judgement; unwise.
"It would be foolish to jump off that cliff without checking if there is a net below."
In plain English: Foolish means acting without thinking about what is smart or right.
"It was foolish to leave your wallet on the table when you were walking through such a crowded street."
Usage: Use "foolish" to describe actions or decisions rather than people, as calling someone directly foolish can sound overly harsh compared to alternatives like "unwise." It is generally informal and less severe than terms like "stupid" or "idiotic," making it suitable for polite criticism.
The word foolish comes from Middle English folisch, which was formed by adding the suffix -ish to the noun fool. It originally meant "having the qualities of a fool."