folly

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A lack of good sense, understanding, or foresight.
2. n. An act or instance of foolishness: regretted the follies of his youth.
3. n. A costly undertaking having an absurd or ruinous outcome.
4. n. An elaborate theatrical revue consisting of music, dance, and skits.
5. n. Obsolete Perilously or criminally foolish action.
6. n. Obsolete Evil; wickedness.
7. n. Obsolete Lewdness; lasciviousness.

Century Dictionary and Cyclopedia

1. n. The character or conduct of a fool; the state of being foolish; weakness of judgment or character, or actions which spring from it; want of understanding; weak or light-minded conduct.
2. n. Something regard for or attention to which is foolish.
3. n. Specifically Conduct morally bad; wickedness; wantonness.
4. n. A costly structure or other undertaking left unfinished for want of means, too expensive to be properly maintained, built in a very ill-chosen place, or the like; an enterprise that exhausts or ruins the projector.
5. n. Synonyms Nonsense, foolishness, senselessness, ridiculousness, extravagance, indiscretion, imbecility. See list under absurdity.
6. To act with folly; act foolishly.
7. Foolish.

Wiktionary

1. n. Foolishness.
2. n. Thoughtless action resulting in tragic consequence.
3. n. A fanciful building built for purely ornamental reasons.

GNU Webster's 1913

1. n. The state of being foolish; want of good sense; levity, weakness, or derangement of mind.
2. n. A foolish act; an inconsiderate or thoughtless procedure; weak or light-minded conduct; foolery.
3. n. Scandalous crime; sin; specifically, as applied to a woman, wantonness.
4. n. The result of a foolish action or enterprise.

WordNet 3.0

1. n. the quality of being rash and foolish
2. n. a stupid mistake
3. n. foolish or senseless behavior
4. n. the trait of acting stupidly or rashly