the state or quality of being foolish; lack of understanding or sense.

a foolish action, practice, idea, etc.; absurdity

the folly of performing without a rehearsal.

a costly and foolish undertaking; unwise investment or expenditure.

Architecture . a whimsical or extravagant structure built to serve as a conversation piece, lend interest to a view, commemorate a person or event, etc.

found esp. in England in the 18th century.

follies, a theatrical revue.

Obsolete . wickedness; wantonness.

noun

judgment , knowledge , seriousness , understanding , wisdom

noun

absurdity , craziness , daftness , dottiness , dumb thing to do , dumb trick , fatuity , foolishness , idiocy , imbecility , impracticality , imprudence , inadvisability , inanity , indiscretion , irrationality , lunacy , madness , obliquity , preposterousness , rashness , recklessness , senselessness , silliness , stupidity , triviality , unsoundness , vice , witlessness , foolery , insanity , nonsense , tomfoolery , zaniness , asininity , desipience , frivolity , indulgence , infatuation , levity , mistake , revue , unwisdom , wantonness , whim