The Collaborative International Dictionary of English v.0.48:

Fool \Fool\, n. [Cf. F. fouler to tread, crush. Cf. 1st Foil.]
   A compound of gooseberries scalded and crushed, with cream;
   -- commonly called gooseberry fool.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fool \Fool\, n. [OE. fol, n. & adj., F. fol, fou, foolish, mad;
   a fool, prob. fr. L. follis a bellows, wind bag, an inflated
   ball; perh. akin to E. bellows. Cf. Folly, Follicle.]
   1. One destitute of reason, or of the common powers of
      understanding; an idiot; a natural.
      [1913 Webster]

   2. 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.
      [1913 Webster]

            Extol not riches, then, the toil of fools. --Milton.
      [1913 Webster]

            Experience keeps a dear school, but fools will learn
            in no other.                          --Franklin.
      [1913 Webster]

   3. (Script.) One who acts contrary to moral and religious
      wisdom; a wicked person.
      [1913 Webster]

            The fool hath said in his heart, There is no God.
                                                  --Ps. xiv. 1.
      [1913 Webster]

   4. One who counterfeits folly; a professional jester or
      buffoon; a retainer formerly kept to make sport, dressed
      fantastically in motley, with ridiculous accouterments.
      [1913 Webster]

            Can they think me . . . their fool or jester?
                                                  --Milton.
      [1913 Webster]

   April fool, Court fool, etc. See under April, Court,
      etc.

   Fool's cap, a cap or hood to which bells were usually
      attached, formerly worn by professional jesters.

   Fool's errand, an unreasonable, silly, profitless adventure
      or undertaking.

   Fool's gold, iron or copper pyrites, resembling gold in
      color.

   Fool's paradise, a name applied to a limbo (see under
      Limbo) popularly believed to be the region of vanity and
      nonsense. Hence, any foolish pleasure or condition of vain
      self-satistaction.

   Fool's parsley (Bot.), an annual umbelliferous plant
      (Aethusa Cynapium) resembling parsley, but nauseous and
      poisonous.

   To make a fool of, to render ridiculous; to outwit; to
      shame. [Colloq.]

   To play the fool, to act foolishly; to act the buffoon; to
      act a foolish part. "I have played the fool, and have
      erred exceedingly." --1 Sam. xxvi. 21.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fool \Fool\, v. i. [imp. & p. p. Fooled; p. pr. & vb. n.
   Fooling.]
   To play the fool.
   [1913 Webster]

   2. To waste time in unproductive activity; to spend time in
      idle sport or mirth; to trifle; to toy.

   Syn: fool around.
        [PJC]

              Is this a time for fooling?         --Dryden.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fool \Fool\, v. t.
   1. To infatuate; to make foolish. --Shak.
      [1913 Webster]

            For, fooled with hope, men favor the deceit.
                                                  --Dryden.
      [1913 Webster]

   2. To use as a fool; to deceive in a shameful or mortifying
      manner; to impose upon; to cheat by inspiring foolish
      confidence; as, to fool one out of his money.
      [1913 Webster]

            You are fooled, discarded, and shook off
            By him for whom these shames ye underwent. --Shak.
      [1913 Webster]

   To fool away, to get rid of foolishly; to spend in trifles,
      idleness, folly, or without advantage.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fool
    n 1: a person who lacks good judgment [syn: fool, sap,
         saphead, muggins, tomfool]
    2: a person who is gullible and easy to take advantage of [syn:
       chump, fool, gull, mark, patsy, fall guy,
       sucker, soft touch, mug]
    3: a professional clown employed to entertain a king or nobleman
       in the Middle Ages [syn: jester, fool, motley fool]
    v 1: make a fool or dupe of [syn: fool, gull, befool]
    2: spend frivolously and unwisely; "Fritter away one's
       inheritance" [syn: fritter, frivol away, dissipate,
       shoot, fritter away, fool, fool away]
    3: fool or hoax; "The immigrant was duped because he trusted
       everyone"; "You can't fool me!" [syn: gull, dupe,
       slang, befool, cod, fool, put on, take in, put
       one over, put one across]
    4: indulge in horseplay; "Enough horsing around--let's get back
       to work!"; "The bored children were fooling about" [syn:
       horse around, arse around, fool around, fool]

Moby Thesaurus II by Grady Ward, 1.0:

291 Moby Thesaurus words for "fool":
   Columbine, Hanswurst, Harlequin, Pantalone, Pantaloon,
   Polichinelle, Pulcinella, Punch, Punchinello, Scaramouch, ament,
   apish, asinine, ass, babe, bamboozle, banter, batty, be foolish,
   be stupid, befool, befooled, beguiled, besotted, birdbrain,
   blockhead, bluff, bonehead, boob, booby, brainless, buffo, buffoon,
   buffoonish, busybody, butt, butt in, byword, byword of reproach,
   cavort, cheat, chouse, chucklehead, chump, cinch, clod, clodpate,
   clodpoll, clown, clown around, cockeyed, come-on, comedian,
   comedienne, comic, con, coquet, cozen, crazy, credulous,
   credulous person, cretin, cull, dabble, dabbler, daffy, daft,
   dally, dawdle, dazed, deceive, defraud, delude, derision,
   dilettante, dimwit, dizzy, dolt, donkey, doodle, dope, doting,
   droll, dumb, dumbbell, dummy, dunce, dupe, easy mark,
   easy pickings, entertainer, fair game, fake, fake out, fall guy,
   farceur, fatuitous, fatuous, featherbrain, featherhead, feign,
   fiddle, fiddle with, fiddle-faddle, fidget with, figure of fun,
   finger with, fish, flaky, fleece, flirt, fond, fool around,
   fool with, foolheaded, foolish, footle, fribble, frivol, frolic,
   fuddled, futile, gaga, gambol, game, gazingstock, get funny, git,
   go haywire, goat, gobe-mouches, goofy, goon, goose, greener,
   greenhorn, greeny, gudgeon, gull, gulled, half-wit, harlequin,
   hoax, hoodwink, horn in, horse around, humbug, idiot, idiotic,
   idle, ignoramus, illiterate, illiterati, imbecile, inane, inept,
   infatuated, innocent, insane, instrument, interfere, interlope,
   intermeddle, invite ridicule, jack-pudding, jackass, jay, jerk,
   jerk off, jest, jester, jestingstock, joke, joker, jokester, josh,
   kid, kid around, know-nothing, kooky, laughingstock, lead on,
   leadpipe cinch, loiter, loon, loony, loser, lowbrow, mad, madman,
   make, make believe, mark, maudlin, meddle with, merry-andrew,
   mess around, middlebrow, mislead, mockery, monkey, monkey around,
   monkey with, mooncalf, moron, moronic, motley, motley fool, mug,
   natural, nincompoop, ninny, ninnyhammer, nit, nitwit, no scholar,
   numskull, nutty, oaf, patsy, pickle-herring, piddle, pigeon,
   pinhead, play, play around, play the buffoon, play the fool,
   play with, plaything, pluck, poop, potter, pretend, prize sap,
   puddinghead, pushover, put one on, putter, rattlebrain, retard,
   romp, sap, saphead, sappy, scatterbrain, schlemiel, schmuck,
   screwy, senseless, sentimental, silly, simple, simpleton,
   sitting duck, smatter, snow, softhead, spoof, stock, stooge,
   string along, stupid, sucker, swindle, take in, tamper,
   tamper with, target, tease, tenderfoot, thoughtless, tinker,
   tomfool, tool, toy, toy with, trick, trifle, trifle with,
   trusting soul, twiddle, twist, twit, unintelligentsia, victim,
   wacky, wanton, wet, witless, zany



The Jargon File (version 4.4.7, 29 Dec 2003):

fool
 n.

    As used by hackers, specifically describes a person who habitually reasons
    from obviously or demonstrably incorrect premises and cannot be persuaded
    by evidence to do otherwise; it is not generally used in its other senses,
    i.e., to describe a person with a native incapacity to reason correctly, or
    a clown. Indeed, in hackish experience many fools are capable of reasoning
    all too effectively in executing their errors. See also cretin, loser,
    fool file.

    The Algol 68-R compiler used to initialize its storage to the character
    string "F00LF00LF00LF00L..." because as a pointer or as a floating point
    number it caused a crash, and as an integer or a character string it was
    very recognizable in a dump. Sadly, one day a very senior professor at
    Nottingham University wrote a program that called him a fool. He proceeded
    to demonstrate the correctness of this assertion by lobbying the university
    (not quite successfully) to forbid the use of Algol on its computers. See
    also DEADBEEF.


The Free On-line Dictionary of Computing (30 December 2018):

FOOL

   Fool's Lisp.  A small Scheme interpreter.

   (ftp://scam.berkeley.edu/src/local/fools.tar.Z).

   (1994-10-04)


The Devil's Dictionary (1881-1906):

FOOL, n.  A person who pervades the domain of intellectual speculation
and diffuses himself through the channels of moral activity.  He is
omnific, omniform, omnipercipient, omniscience, omnipotent.  He it was
who invented letters, printing, the railroad, the steamboat, the
telegraph, the platitude and the circle of the sciences.  He created
patriotism and taught the nations war -- founded theology, philosophy,
law, medicine and Chicago.  He established monarchical and republican
government.  He is from everlasting to everlasting -- such as
creation's dawn beheld he fooleth now.  In the morning of time he sang
upon primitive hills, and in the noonday of existence headed the
procession of being.  His grandmotherly hand was warmly tucked-in the
set sun of civilization, and in the twilight he prepares Man's evening
meal of milk-and-morality and turns down the covers of the universal
grave.  And after the rest of us shall have retired for the night of
eternal oblivion he will sit up to write a history of human
civilization.