a silly or stupid person; a person who lacks judgment or sense.
a professional jester, formerly kept by a person of royal or noble rank for amusement: the court fool.
a person who has been tricked or deceived into appearing or acting silly or stupid: to make a fool of someone.
an ardent enthusiast who cannot resist an opportunity to indulge an enthusiasm (usually prec. by a present participle): He's just a dancing fool.
a weak-minded or idiotic person.