From WordNet (r) 3.0 (2006):
folly
n 1: the trait of acting stupidly or rashly [syn: folly,
foolishness, unwiseness] [ant: wisdom, wiseness]
2: a stupid mistake [syn: stupidity, betise, folly,
foolishness, imbecility]
3: the quality of being rash and foolish; "trying to drive
through a blizzard is the height of folly"; "adjusting to an
insane society is total foolishness" [syn: folly,
foolishness, craziness, madness]
4: foolish or senseless behavior [syn: folly, foolery,
tomfoolery, craziness, lunacy, indulgence]