fool

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who is deficient in judgment, sense, or understanding.
• noun One who acts unwisely on a given occasion.
• noun One who has been tricked or made to appear ridiculous; a dupe.
• noun Informal A person with a talent or enthusiasm for a certain activity.
• noun A member of a royal or noble household who provided entertainment, as with jokes or antics; a jester.
• noun One who subverts convention or orthodoxy or varies from social conformity in order to reveal spiritual or moral truth.
• noun A dessert made of stewed or puréed fruit mixed with cream or custard and served cold.
• noun Archaic A mentally deficient person; an idiot.
• intransitive verb To deceive or trick; dupe.
• intransitive verb To confound or prove wrong; surprise, especially pleasantly.
• intransitive verb To speak or act facetiously or in jest; joke.
• intransitive verb To behave comically; clown.
• intransitive verb To feign; pretend.
• intransitive verb To engage in idle or frivolous activity.
• intransitive verb To toy, tinker, or mess.
• adjective Foolish; stupid.
• idiom (play/act) To act in an irresponsible or foolish manner.
• idiom (play/act) To behave in a playful or comical manner.

from The Century Dictionary.

• noun One who is deficient in intellect; a weak-minded or idiotic person.
• noun One who is deficient in judgment or sense; a silly or stupid person; one who manifests either habitual or occasional lack of discernment or common sense: chiefly used as a term of disparagement, contempt, or self-depreciation.
• noun One who counterfeits mental weakness or folly; a professional jester or buffoon; a retainer dressed in motley, with a pointed cap and bells on his head, and a mock scepter or bauble in his hand, formerly kept by persons of rank for the purpose of making sport. See bauble.
• noun Figuratively, a tool, toy, sport, butt, or victim: as, to be the fool of circumstances.
• noun A wanton, bad, or wicked person.
• noun A conical paper cap which dunces at school are sometimes compelled to wear by way of punishment.
• noun To act like one void of understanding.
• noun Synonyms and Simpleton, ninny, dolt, witling, blockhead. driveler.
• noun Harlequin, clown, jester. See zany.
• Foolish; silly.
• To play the fool; act like a weak-minded or foolish person; potter aimlessly or mischievously; toy; trifle.
• To play the buffoon; act as a fool or jester.
• To make a fool of; expose to contempt; disappoint; deceive; impose on.
• To make foolish; infatuate.
• To beguile; cheat: as, to fool one out of his money.
• noun A light paste of flour and water, like pie-crust.
• noun A sort of custard; a dish made of fruit crushed and scalded or stewed and mixed with whipped cream and sugar: as, gooseberry fool.

from the GNU version of the Collaborative International Dictionary of English.

• noun A compound of gooseberries scalded and crushed, with cream; -- commonly called gooseberry fool.
• intransitive verb To play the fool; to trifle; to toy; to spend time in idle sport or mirth.
• noun One destitute of reason, or of the common powers of understanding; an idiot; a natural.
• noun A person deficient in intellect; one who acts absurdly, or pursues a course contrary to the dictates of wisdom; one without judgment; a simpleton; a dolt.
• noun (Script.) One who acts contrary to moral and religious wisdom; a wicked person.
• noun One who counterfeits folly; a professional jester or buffoon; a retainer formerly kept to make sport, dressed fantastically in motley, with ridiculous accouterments.
• noun See under April, Court, etc.