Foolish means showing bad judgment, or unwise. A foolish decision, feel foolish, foolish pride.
It criticises the judgement rather than the intelligence — a clever person can do something foolish, which is most of history. Feel foolish means embarrassed at your own expense. Penny wise and pound foolish is the fixed phrase for saving small and losing large. Note foolishly, foolishness; and that fool comes from the Latin for a bellows, meaning a windbag.
1adjectivefoolishShowing bad judgment.
“It was foolish of me to leave my bag in the car with the doors unlocked.”
foolish is a quality of poor judgement.
Middle English folisch is fool plus -ish, from Old French fol, from Latin follis, a bellows or bag of wind. A fool was a windbag before he was a simpleton.
Middle English
folisch
English, today
foolish
From Middle English folisch; equivalent to fool + ish.
Etymology from Wiktionary, CC BY-SA