- folly [fäl′ē]n.pl. follies [ME folie < OFr < fol: see FOOL1]1. a lack of understanding, sense, or rational conduct; foolishness2. any foolish action or belief3. any foolish and useless but expensive undertaking4.a) Obs. wickedness or evil; also, lewdnessb) action that ends or can end in disaster: See also FOLLIES
English World dictionary. V. Neufeldt. 2014.