From the second edition (1989):
fool, n.1 and a.
(fuːl) Forms: 3–4 fol, (3 folle), 3–6 fole, (4 foyl), 4–6 foule(e, (4 fowle), 4–7 foole, (6 foolle), 4–9 Sc. fule, 5–6 full(e, 5–7 Sc. fuil(l, -yll, (5 fwle), 4– fool. [ME. fōl n. and adj., ad. OF. fol n. and adj. (mod.F. fou n., insane person, madman, fou adj. masc., before vowel fol, fem. folle), corresponding to Pr. fol, folh, It. folle:—L. follem, follis, lit. ‘bellows,’ but in late popular Lat. employed in the sense of ‘windbag,’ empty-headed person, fool.]

A. n. I. 1. a. One deficient in judgement or sense, one who acts or behaves stupidly, a silly person, a simpleton. (In Biblical use applied to vicious or impious persons.)
The word has in mod.Eng. a much stronger sense than it had at an earlier period; it has now an implication of insulting contempt which does not in the same degree belong to any of its synonyms, or to the derivative foolish. Cf. F. sot.

c1275 Lay. 1442 Cniþt þou art mochel fol. 1340 Hampole Pr. Consc. 126 Elles es he a fole and noght wise. 1398 Trevisa Barth. De P.R. vi. xvii. (1495) 203 Telle a fole his defawte, and he shall hate the. 1481 Caxton Godfrey xxv. 57 There ben more fooles than wysemen. a1550 Christis Kirke Gr. xxii, For faintness tha forfochtin fulis Fell doun lyk flauchtir fails. 1612 Dekker If it be not good, Prol., Fooles by lucky Throwing, oft win the Game. 1709 Pope Ess. Crit. 625 For Fools rush in where Angels fear to tread. 1773 Mrs. Chapone Improv. Mind (1774) II. 111 Unless you improve your mind‥you will be an insignificant fool in old age. 1816 Scott Antiq. xliii, ‘Mony a wise man sits in a fule's seat, and mony a fule in a wise man's, especially in families o' distinction.’ 1881 Besant & Rice Chapl. Fleet I. 144 No doubt, there have been fools before.

b. Phrase. to be a fool to: to be every way inferior to, to be as nothing compared to.

1596 Shakes. Tam. Shr. iii. ii. 159 Tut, she's a Lambe, a Doue, a foole to him. 1791 ‘G. Gambado’ Ann. Horsem. xvii. (1809) 137 Childers would have been a fool to him. 1885 Rider Haggard K. Solomon's Mines 79 The Black Hole of Calcutta must have been a fool to it.

c. Used as a term of endearment or pity. Obs.

c1530 Beaut. Women in Hazl. Dodsley I. 71 How say ye now by this, little young fool? a1586 Sidney Astrophel & Stella lxxiii, O heau'nly foole, thy most kisse-worthy face [etc.]. 1611 Shakes. Wint. T. ii. i. 118 Doe not weepe (goode Fooles) There is no cause.

d. In various proverbial expressions.

c1400 Rom. Rose 5266 A fooles belle is soone runge. 1539 Taverner Erasm. Prov. (1552) 4 A foles bolt is soone shotte. 1546 J. Heywood Prov. (1867) 46 There is no foole to the olde foole. 1563 B. Googe Epit. N. Grimaold Eglogs, etc. (Arb.) 74 But Fortune fa[u]ours Fooles as old men saye. 1606 Holland Sueton. Annot. 16 A foole or a physition. c1645 Howell Lett. I. v. xxxix, A fool and his money is soon parted. 1670 Ray Prov. 91 Fools build houses, and wise men buy them. 1721 Kelly Sc. Prov. 101 Every Man at thirty is a Fool or a Physician.

2. a. One who professionally counterfeits folly for the entertainment of others, a jester, clown.
The ‘fool’ in great households was often actually a harmless lunatic or a person of weak intellect, so that this sense and sense 4 are often hard to distinguish.

?1370 Robert Cicyle in Nugæ Poet. (1844) 54 Lyke a fole and a fole to bee, Thy babulle schalle be thy dygnyte! c1440 Ipomydon 1643 He semyd a fole‥Bothe by hede and by atyre. 1532 Privy Purse Exp. Hen. VIII, 205 For making of gere for the kinges fole xxx s. 1609 Dekker Gulls Horne-bk. Proem, Wks. (Grosart) II. 205 He may be‥his crafty foole, or his bawdy Jester. 1651 Brome Joviall Crew v. Wks. 1873 I. 451 To beg the next Fool-Royal's place that falls. 1691 Luttrell Brief Rel. (1857) II. 311 Mr. Graham, the fool in King James time. 1847 L. Hunt Jar Honey vi. (1848) 75 He had all the humiliations‥of the cap and bells, and was the dullest fool ever heard of.

b. to play the fool: to act the part of a fool or jester; hence gen. to act like a fool (sense 1).

c1532 G. Du Wes Introd. Fr. in Palsgr. 939 To plee the fole, baguenauder. 1579 Fulke Heskins' Parl. 295 He playeth the foole with that bable. 1659–60 Pepys Diary 28 Feb., I staid up a little while, playing the fool with the lass of the house. 1722 De Foe Relig. Courtsh. i. i, I advise you not to play the fool with me any longer. 1847 James J. Marston Hall viii, The parliament was playing the fool in Paris.

c. Feast of Fools [=med.L. festum stultorum]: properly the burlesque festival which in the Middle Ages was sometimes celebrated in churches on New Year's Day; hence in various allusive uses.

c1320 Seuyn Sag. (W.) 2748 Sire, hastou owt herde the geste, Whi men made folen feste? 1609 Dekker Gulls Horne-bk. Proem. Wks. (Grosart) II. 209 To the intent I may aptly furnish this feast of Fooles.

3. One who is made to appear a fool; one who is imposed on by others; a dupe. Now somewhat arch., exc. in phrases to make a fool of (formerly also †to put the fool on), to dupe, befool; to be a fool for one's pains, to have one's labour for nothing.

c1440 Jacob's Well 81 A nunne, þat‥made here as a fool, and obeyid here to alle here sustren as here fool. 1579 Lyly Euphues (Arb.) 89 Bicause I was content to be his Friend, thought he me meete to be made his Foole. 1592 Shakes. Rom. & Jul. iii. i. 141, I am Fortunes foole. 1625 Cooke Pope Joan in Harl. Misc. (Malh.) IV. 28 The dean made a fool of the alderman. a1684 Leighton Comm. 1 Peter i. 3 Worldly hopes‥put the fool upon a man. 1715 De Foe Fam. Instruct. i. iv, I won't be made a fool of. 1850 Tennyson In Mem. iv, Thou shalt not be the fool of loss. Mod. He is the fool of circumstances.

4. One who is deficient in, or destitute of reason or intellect; a weak-minded or idiotic person. Obs. exc. in natural fool or born fool, a born idiot (now rare exc. as a mere term of abuse). to beg (a person) for a fool: see beg 5a.

1540 Act 32 Hen. VIII, c. 46 Ideottes and fooles naturall. 1566 Nashe Saffron Walden Civb, Fooles‥(especiallie if they bee naturall fooles) are suted in long coates. 1601 Shakes. All's Well iv. iii. 213 He was whipt for getting the Shrieues fool with childe, a dumbe innocent that could not say him nay. 1609 Skene Reg. Maj. 37 The warde and custodie of lands and tenements perteining to naturall fuilis, be the law sould perteine to the King. 1670 R. Lassels Voy. Italy ii. 212 The Pazzorella, where they keep madmen and fooles. 1708 Ockley Saracens (Bohn 1848) 326 Towards the latter end of his days, he did really turn fool. 1824 R. Crabb Tales 142 He became well in his health; but he remained quite a fool for the rest of his life!

II. In combinations.

5. General combinations; a. simple attributive, as fool-cunningness, fool-trap, fool-work.

a1834 Coleridge Lit. Rem. III. 198 This conceit‥was just suited to James's *fool-cunningness. 1691 Dryden K. Arthur Prol. 27 Bets at the first were *fool-traps. 1883 W. Rein Life Luther xxii. 178 Hoods and tonsure, eating and drinking, and similar *fool-work.

b. appositive, as fool-dancer, fool-fury, fool-gallant.

1887 D. C. Murray & Herman One Trav. Returns vii. 100 A *fool-dancer, in his ochre-smeared kilt and head~dress‥sprang and contorted for a reward. 1850 Tennyson In Mem. cxxv, Ev'n tho' thrice again The red *fool-fury of the Seine Should pile her barricades with dead. 1714 Pope Wife Bath 95 Or else her wit some *fool-gallant procures.

c. objective, as fool-catcher, fool-doctor, fool-taker; fool-frighting adj.

1594 Nashe Vnfort. Trav. Wks. (Grosart) V. 39 They‥in fine left mee and my fellowes (their *foole-catchers) Lords of the field. a1624 Breton Figure Foure (Grosart) 5/2 A Foole-catcher, and a Cony-catcher. 1760 Jortin Erasm. II. 170 None are greater Fools than they, who set up for *Fool-Doctors. a1720 Sheffield (Dk. Buckhm.) Wks. (1753) I. 177 Fiery meteors, and *fool-frighting ghosts. c1600 Nashe (Grosart), *Foole-taker.

d. instrumental and originative, as fool-born, fool-frequented, fool-renowned adjs.

1597 Shakes. 2 Hen. IV, v. v. 59 Reply not to me, with a *Foole-borne Iest. 1780 Cowper Table-t. 756 The *fool-frequented fair of vanity. 1742 Pope Dunc. iv. 371 Mummius *Fool-renown'd.

e. similative, as fool-bold, fool-fat, fool-fine, fool-heady, fool-holy adjs.; fool-like, fool-wisely advs. (Some of these imitate foolhardy, and may perhaps better be referred to the adj.)

1549 Leland Itin. Fiijb, Some in corners hath bene *folebolde. 1613 Chapman Revenge Bussy D'Ambois Plays 1873 II. 113 Men thither come to laugh and feede *fool-fat. 1593–4 Sylvester Profit Imprisonm. 638 Depending oft on his foole-fat-feeding word. 1603 H. Crosse Vertues Commw. (1878) 64 To know the price of Sattin and Veluet, and toies to make him *fool-fine. 1611 Speed Hist. Gt. Brit. vi. i. §5. 184 Begging pardon for his *foole-heady forwardnesse. 1592 Greene Groatsw. Wit Biij, So *foole holy as to make scruple of conscience where profit presents itselfe. 1842 Whitehead R. Savage (1845) II. viii. 286 *Foole-like, I forgot myself. 1605 Camden Rem. (1637) 84 But *foole-wisely have some Peters, called themselves Pierius. 1611 W. Sclater Key (1629) 111 Some of them resoluing, foole wisely, that images are to be worshipped.

6. Special comb, as fool-bane, poison for fools; fool-begged a., ? foolish, idiotic (cf. beg 5a); fool-duck (U.S.), the ruddy duck, Erismatura rubida; †fool-fangle, a silly trifle; †fool-finder, slang (see quot.); fool-fish (U.S.) a poplar name for certain fishes (see quots.); †fool-happy a., lucky without judgement or contrivance; fool-hen (U.S.), see quot.; fool-plough (see quot. 1777); †fool- or fool's-rack, ‘a‥pernicious spirit, in which‥the stinging sea-blubber was mixed’ (Yule); †fool-taken a., ‘taken in’ like fools; †fool-taking vbl. n., a method of cozening.

1679 Dryden Troilus & Cr. Epil. 10 'Twere worth our cost to scatter *fool-bane here. 1590 Shakes. Com. Err. ii. i. 41 This *foole-beg'd patience in thee will be left. 1647 Ward Simpl. Cobler 30 Ape-headed pullets, which invent Antique *foole-fangles, meerly for fashion‥sake. 1796 Grose Dict. Vulg. Tongue (ed. 3), *Fool finder, a bailiff. 1842 J. E. De Kay Nat. Hist. New York iv. 335 Our fishermen apply to it [Monocanthus broccus] the whimsical name of *Fool-fish, in allusion to‥its absurd mode of swimming. 1888 Riverside Nat. Hist. III. 279 The Pleuronectes glaber, which is called fool-fish at Salem, because they are easily decoyed. 1590 Spenser F.Q. i. vi. 1 His *foolhappie over~sight. 1885 T. Roosevelt Hunting Trips iii. 90 In the early part of the season the young [grouse], and indeed their parents also, are tame and unsuspicious to the very verge of stupidity, and‥are often known by the name of *‘fool-hens’. 1777 Brand Pop. Antiq. xiv. 175 The *Fool Plough goes about, a Pageant that consists of a Number of Sword Dancers, dragging a Plough with Music [etc.]. 1698 Fryer Acc. E. Ind. & P. i. 68 *Fool Rack, Brandy made of Blubber or Carvil, by the Portugals. 1608 Dekker Belman Lond. Hivb, *Foole-taking‥is done seuerall wayes [described at length]. Ibid., *Foole-taken.

7. Comb. with genitive fool's: a. obvious combinations (sense 2), as fool's ba(u)ble, fool-colours, fool-staff. Also in phr. †to come home by Fool's acre.

1603 H. Crosse Vertues Commw. (1878) 63 They‥come home by Need-ham crosse, and *fooles acre. 1578 Lyte Dodoens iii. lxxix. 428 Fashioned like a *fooles bable. 1728 Pope Dunc. i. 84 And with her own *fools-colours gilds them all. 1692 Washington tr. Milton's Def. Pop. Pref. (1851) 17 You‥deserve to have your Bones well-thrash'd with a *Fool's staff.

b. Special comb., as fool's crochet (see quot.); fool's errand: see errand 2 c; †fool's fire, a will o'-the-wisp, Ignis fatuus; fool's gold, iron pyrites; fool's haste, foolish precipitation; fool's-head, a head void of sense or intelligence; also, a foolish person; (cf. sheep's-head); fool's hood, the hood worn by a fool or jester; also, a hood resembling this, worn in the seventeenth century; fool's mate (Chess): see mate. Also foolscap, fool's-coat, fool's paradise.

1882 Caulfeild & Saward Dict. Needlework, *Fool's Crochet, a name sometimes given to Tricot. 1631 Widdowes Nat. Philos. (ed. 2) 16 Fiery Dragons, darke streames, *fooles fire, and such like fiery Meteors. 1882 Boston Jrnl. Chem. Feb. 16/3 *‘Fool's gold’. 1827 Scott Jrnl. 12 Jan., I wish it may not prove *fool's haste, yet I take as much pains too as is in my nature. 1577 Breton Floorish vpon Fancie, etc. (Grosart) 24/2 In the ende‥Shee makes him see a *Fooles head of his owne. 1598 Shakes. Merry W. i. iii. 134. 1650 R. Stapylton Strada's Low C. Warres iv. 78 The Low-countrey Lords were not fools-heads. 1597 Gerarde Herbal i. xcix. 159 In shape like to a *fooles hood or cocks-combe wide open. 1647 R. Stapylton Juvenal viii. 191 When nightly, thy adulterous blood Conceales it's blushes in a French fooles-hood.

c. esp. in plant-names, as †fool's ballocks, an old name for Orchis Morio; fool's cicely = fool's parsley; fool's (water) cress (see quot. 1878); fool's parsley, a poisonous weed, the Lesser Hemlock (Æthusa Cynapium); hence, a book-name of the genus Æthusa; †fool's stones, an old name for Orchis Morio and O. mascula.

1578 Lyte Dodoens ii. lvi. 222 This second kinde [of Orchis] is called‥in English‥*Fooles Balloxe. 1796 Withering Brit. Plants (ed. 3) II. 305 Æthusa Cynapium‥*Fool's Cicely, Lesser Hemlock. 1861 Mrs. Lankester Wild Flowers 31 The *Fool's-Cress, as it is called (Sium nodiflorum). 1878 Britten & Holland Plant-n., Fool's Water Cress, Helosciadium nodiflorum‥Because those who are ignorant or unobservant may mistake it for water cress. 1755 Gentl. Mag. XXV. 69 The lesser Hemlock, or *Fool's Parsley. 1816–20 Green Univ. Herbal I. 64 Æthusa Fatua, Fine-leaved Fool's Parsley. 1597 Gerarde Herbal i. xcix. §5. 159 The male *Foole stones hath fiue‥long, broad and smooth leaues. Ibid. The female Fooles stones hath also smooth narrow leaues.

B. adj. Foolish, silly. Now colloq. (freq. in U.S.).
By the late 19th cent. this use was obs. in the U.K., exc. Sc. and dial. and vulgar (the vulgar use being prob. a new formation from the n.).

a1225 Ancr. R. 54 Þe holi Gost lette writen one boc uor to warnie wummen of hore fol eien. a1240 Ureisun in Cott. Hom. 200 Me nis he fol chepmon, ðet buð deore a woc þing? 1297 R. Glouc. (1724) 568 Þis lokinge was riȝt fol in such destresse iwis. c1314 Guy Warw. (A.) 380. 10 Ich wene þou art a fole musard! c1400 Destr. Troy 13841 Hit fell hym by fortune of a foole end. c1450 Mirour Saluacioun 271 The wise virgines yt oele vnto the fole maydens denyed. 1481 Caxton Tulle of Old Age, Olde age is grevous‥to the fole old man. 1541 R. Copland Galyen's Terap. 2 Dj, O foole and imprudent Thessalus. 1580 R. Harvey Pl. Perc. (1590) 22 Let the wisest be the forwardest, and the most foole the frowardest. 1681 S. Colvil Whigs Supplic. (1751) 130 Fighting is a fool thing. a1776 Song in Herd Collect. II. 192 The fool-thing is oblig'd to fast Or eat what they've refus'd. 1805 L. Dow Jrnl. (1806) II. i. 76, I showed the contrast of a gentleman and a fool deist. 1815 Scott Guy M. xxxix, ‘They couldna hae sell'd the auld inheritance for that fool-body's debts.’ 1823 Galt Entail II. iii. 22 A fool posture‥and no very commodious at this time. 1854 M. J. Holmes Tempest & Sunshine ii. 25 Tempest‥can hardly wait till I'm dead before she spends my money on fool fixins. 1862 S. Hale Lett. (1919) 13 Everybody talking such fool nonsense as sometimes almost to prevent digestion. 1896 M. Corelli Mighty Atom xvi. 335 My fool tears a-flowin' on her coffin. 1902 W. N. Harben Abner Daniel 2 Oh, Alan, don't you see he's goin' to ruin us with his fool notions? 1912 R. A. Wason Friar Tuck xxiii. 165 It was the foolest lookin' group I was ever part of. 1924 W. M. Raine Troubled Waters xxiii. 245 You've heard that fool story about Norma and Mac. 1932 E. Wilson Devil take the Hindmost ix. 104 The local banks have failed through the speculations of some fool gambler. 1951 ‘J. Wyndham’ Day of Triffids iv. 85 You never can tell what fool carelessness may go on.