Foolish people are silly or senseless, and when you do something foolish, it's clearly unwise or irrational. Sitting on the hood of a car while your friend is driving is a foolish thing to do.

Things that show a lack of judgment are foolish, like cheating on a test or running into the street after a basketball. Foolish decisions at work can cost you your job, and foolish comments can hurt people's feelings. Foolish is a 14th century word that comes from fool, a person who's unwise. The Latin root, follis, means "bellows" or "leather bag." The "silly person" meaning comes from the figurative idea of a "windbag."

Definitions of foolish
  1. adjective
    devoid of good sense or judgment
    foolish remarks”
    “a foolish decision”
    inadvisable, unadvisable
    not prudent or wise; not recommended
    ill-advised, unadvised
    without careful prior deliberation or counsel
    not politic
    not prudent or wise
    absurd, cockeyed, derisory, idiotic, laughable, ludicrous, nonsensical, preposterous, ridiculous
    incongruous;inviting ridicule
    asinine, fatuous, inane, mindless, vacuous
    devoid of intelligence
    cockamamie, cockamamy, goofy, sappy, silly, wacky, whacky, zany
    ludicrous, foolish
    absurd or silly because unlikely
    harebrained, insane, mad
    very foolish
    ill-conceived, misbegotten, misguided
    poorly conceived or thought out
    rattlebrained, rattlepated, scatterbrained, scatty
    lacking sense or discretion
    showing or resulting from lack of judgment or wisdom
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    having or prompted by wisdom or discernment
    worthy of being recommended or suggested; prudent or wise
    advised, well-advised
    having the benefit of careful prior consideration or counsel
    marked by artful prudence, expedience, and shrewdness
    careful and sensible; marked by sound judgment
    all-knowing, omniscient
    infinitely wise
    perspicacious, sagacious, sapient
    acutely insightful and wise
    resembling an owl; solemn and wise in appearance
    characterized by wisdom, especially the wisdom of God
    having wisdom that comes with age and experience
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  2. adjective
    having or revealing stupidity
    synonyms: anserine, dopey, dopy, gooselike, goosey, goosy, jerky
    lacking or marked by lack of intellectual acuity
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