fool¹ / foōl/ • n. a person who acts unwisely or imprudently; a silly person: what a fool I was to do this. ∎ hist. a jester or clown, esp. one retained in a noble household. ∎ inf. a person devoted to a particular activity: he is a running fool. ∎ archaic a person who is duped.• v. [tr.] trick or deceive (someone); dupe: he fooled nightclub managers into believing he was a successful businessman she had been fooling herself in thinking she could remain indifferent. ∎  [intr.] act in a joking, frivolous, or teasing way: I shouted at him impatiently to stop fooling around. ∎  [intr.] (fool around) engage in casual or extramarital sexual activity.• adj. inf. foolish or silly: that damn fool waiter.PHRASES: be no (or nobody's) fool be a shrewd or prudent person.make a fool of trick or deceive (someone) so that they look foolish. ∎  (make a fool of oneself) behave in an incompetent or inappropriate way that makes one appear foolish.play (or act) the fool behave in a playful or silly way.you could have fooled me! used to express cynicism or doubt about an assertion: “Fun, was it? Well, you could have fooled me!”PHRASAL VERBS: fool with toy with; play idly with: I like fooling with cameras. ∎  tease (a person): we've just been fooling with you.fool² • n. chiefly Brit. a cold dessert made of puréed fruit mixed or served with cream or custard: raspberry fool with cream.

fool a fool and his money are soon parted proverbial saying, late 16th century.
a fool at forty is a fool indeed proverbial saying, early 16th century, from the poet Edward Young (1683–1765), and meaning that someone who has not learned wisdom by the age of forty will never learn it. A mid 16th-century sermon has the same idea in reference to the age of forty-one, ‘And he that hath not learned some experience or practice and trade of the world by that age will never be wise.’
a fool may give a wise man counsel sometimes used as a warning against overconfidence in one's judgement; saying recorded from the mid 14th century.
fool me once, shame on you; fool me twice, shame on me if someone is deceived twice their own stupidity is to blame; saying recorded from the early 17th century (in the earliest versions, the verb is deceive).
fool's errand a task or activity that has no hope of success.
fool's gold a brassy yellow mineral that can be mistaken for gold, especially pyrite.
fool's paradise a state of happiness based on a person's not knowing about or denying the existence of potential trouble.
there's no fool like an old fool often used to suggest that the folly of an older person is particularly worthy of castigation. The saying is recorded from the mid 16th century.

see also fools, a man who is his own lawyer has a fool for a client, more people know Tom Fool than Tom Fool knows.

fool1
A. one deficient in judgement or sense XIII; professional jester, clown XIV;

B. adj. foolish XIII; now only (exc. dial.) as attrib. use of the sb. ME. fōl sb. and adj. — OF. fol (mod. fou mad) :- L. follis bellows, inflated ball, (later fig.) ‘windbag’, empty-headed person.
Hence fool vb. play the fool, make a fool of XVI. foolery XVI. foolhardy XIII. — OF. folhardi ‘foolish-bold’. foolscap (fool's cap) cap of a professional fool; folio paper of a kind that orig. bore a watermark representing a fool's cap. XVII.

fool2 †clotted cream XVI; dish composed of crushed fruit with cream, etc. XVIII. perh. transf. use of prec. suggested by trifle.

fool A purée of fruit with cream or custard.