As a Noun: 1. Behaviour which is unintelligent, ignorant, unfair, or illogical. English = foolishness, craziness, stupidity. As a Verb or Adjective: 1. To behave in a unintelligent, ignorant, unfair, or illogical way. English = (be) foolish, (be) stupid, (be) crazy, (be) silly, (be) nuts.