From the second edition (1989):
clover, n.
(ˈkləʊvə(r)) Forms: 1 clafre, clæfre, clæfra, 3 clouere, 5 cleure, 5–7 claver, 6– clover. (Also 6 Sc. clauir, -yr, 8–9 claver.) [The form clover is very rare bef. 1600 (one example of clouere c 1265), and did not prevail much bef. 1700; the usual ME. and 16th c. form was claver. The earliest OE. glossaries have clabre, clafre; late WSax. had clæfre fem. Cf. MLG. klêver, klâver masc., LG. kláver, klêwer, klêber, EFris. klafer, kläfer, klefer, NFris. kliawar m., Du. klaver f., Da. klever, klöver, Norw. klöver, klyver, Sw. klöfwer masc. The vowel relations of some of these are not clear; but it appears certain that the earliest Eng. form was cláƀre, cláfre wk. f.:—OTeut. type klaiƀrôn-, app. a compound having its first element identical with OHG. chlêo, -wes (MHG. klê -wes, modG. klee) masc. ‘clover’, and its latter part a worn-down form of some unidentified word. The prevalent ME. claver app. represents a form clæfre with shortened vowel (cf. never:—nǽfre), while the current clover represents the OE. cláfre, retained in some dialect, whence it at length spread out and became the standard form.]

1. a. The common name of the species of Trefoil (Trifolium, family Leguminosæ), esp. T. repens and T. pratense, both largely cultivated for fodder.

α c1000 Ælfric Voc. in Wr.-Wülcker 134/42 Calta, uel trifillon, clæfre. c1000 Sax. Leechd. I. 172 Þysse wyrte‥þe man crision & oðrum naman clæfre nemneð. a1100 Voc. in Wr.-Wülcker 323/29 Uiola, clæfre. Ibid. 408/36 Fetta, clæfra. ?a1400 Morte Arth. 3241 The close‥With clauer and clereworte clede euene ouer. c1450 Alphita (Anecd. Oxon.) 186/2 Trifolium quando simpliciter ponitur, anglice dicitur cleure. 1513 Douglas Æneis xii. Prol. 116 The clavyr, catcluke and the cammamyld. 1562 Turner Herbal ii. 26b, A clauer or threeleued grasse. 1636 G. Sandys Paraphr. Ps. lxv. (1648) 108 The Desert with sweet Claver fils. 1649 W. Blithe Eng. Improv. Impr. xxvi. (1652) 178 There are so many sorts of Claver, as would fill a volume, I shall onely speak of the great Claver, or Trefoyl we fetch from Flaunders. 1672 Grew Philos. Hist. Plants §11 All kinds of Trefoyls, as Melilot, Fœnugreek, and the common Clavers themselves. 1699 Evelyn Acetaria 19 Clavers‥are us'd in Lenten Pottages. 1794 Burns Country Lassie i, While claver blooms white o'er the lea.

[Claver is the form in B. Googe, Lyte, Gerarde, Cotgrave, Surflet & Markham, Bacon, Coles, Parkinson, Salmon.]
β 1599 Shakes. Hen. V, v. ii. 49 The euen Meade, that erst brought sweetly forth The freckled Cowslip, Burnet, and greene Clouer. 1612 Drayton Poly-olb. xxv. 110 Like the penny-grass, or the pure clover. 1697 Dryden Virg. Georg. iii. 232 Where Nature shall provide Green Grass and fat'ning Clover for their Fare. a1763 Shenstone Poems Wks. 1764 I. 235 In russet robes of clover deep. 1846 Baxter Libr. Pract. Agric. II. 31 The effect of coal ashes is most remarkable when applied to clovers growing on sands.

b. With qualifying words, indicating the different species: esp. clustered clover, Trifolium glomeratum; red or meadow clover (also broad clover, clover-grass), Trifolium pratense, and white or Dutch clover, T. repens. Also alsike c., T. hybridum; cow clover, T. medium and T. pratense; crimson clover or carnation c., T. incarnatum; hare's-foot c., Trifolium arvense; hop c., T. procumbens; strawberry c., T. fragiferum; trefoil clover or zig-zag c., T. medium; yellow c., T. procumbens and T. minus.

a800 Erfurt Gloss. 250 Calta, rede clabre; 254 Calesta, huitti clabre. a800 Corpus Gloss. 375 Calta, reade clafre; 377 Calcesta, huite clafre. c1000 Sax. Leechd. II. 312 read clæfre. Ibid. 326 Hwite clæfran wisan. c1265 Voc. in Wr.-Wülcker 556/33 Trifolium, trifoil, wite clouere. 1794 Martyn Rousseau's Bot. xxv. 367 Purple Trefoil, Honeysuckle Trefoil, or Red Clover. Ibid. White Trefoil, commonly called Dutch Clover. 1858 G. Bentham Handbk. Brit. Flora 168 Clustered Clover. Trifolium glomeratum. 1884 E. P. Roe in Harper's Mag. July 247/1 They began with red-top clover. 1921 H. Guthrie-Smith Tutira xix. 171 Lastly appeared Clustered clover (Trifolium glomeratum). 1960 Ary & Gregory Oxf. Bk. Wild Flowers 114/2 Clustered Clover.‥ An uncommon annual‥with tiny, unstalked purple-pink flower-heads.

c. humorously as a term of endearment.

1500–20 Dunbar In secreit place 29 Quod he, ‘My claver, and my curldodie’.

2. Applied in different localities, with qualifying word prefixed, to many plants of the same order, or with similar characters; as bird's-foot c., cat's c., Lotus corniculatus; Calvary clover, Medicago Echinus; heart c., spotted c., Medicago maculata; yellow c., Medicago lupulina; horned c., snail c., species of Medicago; Bokhara c., Melilotus vulgaris; †garden c., Melilotus cærulea; hart's c., king's c., plaister c., Melilotus officinalis; marsh c., Menyanthes trifoliata; cuckoo's c., gowk's c., lady's c., sour c., Oxalis acetosella; thousand-leaved c., Achillea Millefolium; Soola clover or Maltese c., Hedysarum coronarium. Also in U.S.: bush c., Lespedeza; prairie c., Petalostemon; sweet c., Melilotus.

1548 Turner Names of Herbes s.v. Medica, It hath leaues like a clauer and horned cods‥Therefore it maye be called in englishe horned Clauer or snail Trifoly. Ibid. 49 Lotus vrbana‥it maye be named in english gardine Clauer or gardine Trifoly. 1578 Lyte Dodoens iv. xxxvii. 496 Turner calleth Lotus vrbana in English, Garden or Sallet Clauer: we may call it sweete Trefoyl, or three leaued grasse. 1616 Surfl. & Markh. Country Farme 565 The good husbandman must be carefull to gather and reserue seed of this snaile clauer. 1626 Bacon Sylva (1677) §493 They make it a piece of the wonder, that Garden Claver will hide the Stalk, when the Sun sheweth bright. 1640 Parkinson Theat. Bot. 720 (Britten & H.) In some places they call it Hart's Claver, because if it grow where stagges and deere resort, they will greedily feede thereon‥In English wee call it generally King's Claver as the chiefest of all other three-leaved grasses. 1794 Martyn Rousseau's Bot. xxv. 368 We have one variety [of Medicago] very common wild, called Heart-Clover from the form of the leaves, which are also generally spotted.

3. Phrase. to live (or be) in clover: ‘to live luxuriously; clover being extremely delicious and fattening to cattle’ (J.).

1710 Brit. Apollo II. No. 105. 3/1, I liv'd in Clover. a1746 Ogle (J.), Well, Laureat, was the night in clover spent? a1839 Praed Poems (1864) I. 136 You might have lived your day in clover. 1856 R. Vaughan Mystics (1860) II. viii. ix. 102 He has been sometimes in clover as a travelling tutor, sometimes he has slept and fared hard.

4. attrib. and Comb., as clover-bloom, clover-blossom, clover-blow, clover-farm, clover-field, clover-flower, clover-hay, clover-head, clover-hill, clover-leaf, clover-seed; Clover Club, the name of a club in Philadelphia, used to designate a cocktail made from gin, white of egg, lemon or lime juice, and grenadine; clover-dodder, Cuscuta Trifolii; clover-fern Austral., nardoo; clover-hay worm, the larva of a small moth, Asopia costalis, very destructive to clover-hay in North America; clover-huller, a machine for separating clover-seed from the hulls; clover-leaf, a system of intersecting roads from different levels, in form resembling the leaf of clover; freq. attrib.; clover-leaf sight (see quot.); clover-ley, -lay (see quots.); clover-sheller = clover-huller above; clover-sick a., (of land) that has been too continuously kept under clover and that will no longer grow or support it; hence clover-sickness; clover summer, fig. an exceptional time; clover-thrasher = clover-huller above; clover-weevil, a small weevil, Apion apricans, which feeds on the seeds of clover. Also clover-grass.

1845 Longfellow Gleam Sunshine vi, The *clover-blossoms in the grass. 1867 Emerson May-day, etc. Wks. (Bohn) III. 411 Columbine and *clover-blow. 1925 E. Wallace King by Night xlii. 186 *Clover Club cocktails, John. 1931 A. Powell Afternoon Men xiv. 147 He‥went to the bar and ordered two clover-clubs and a sidecar. 1847 Emerson Poems, Wood-notes I. 422 It smells like a *clover-farm. 1878 R. B. Smyth Abor. Victoria I. 209 They seem to have been unacquainted, generally, with the use, as a food, of the *clover-fern, Nardoo. 1840 J. Morton Glouc. Farm Rep. 16 in Libr. Usef. Knowl., Husb. III, They are‥put to run in a fallow-field, if there is not a pasture or *clover-field. 1870 ‘Fanny Fern’ Ginger-Snaps 257, I shall shortly find a clover field where I intend to bury my disgusted nose until October. 1612 Drayton Poly-olb. xv. 241 The Crow-flower, and thereby the *Clouer-flower they stick. 1748 J. Eliot Field-Husb. 17 He that raiseth *Clover Hay, need not be afraid of the expence of Seed. 1840 J. Morton Glouc. Farm Rep. 18 in Libr. Usef. Knowl., Husb. III, Good rye-grass and clover-hay is best for them. 1843 ‘R. Carlton’ New Purchase 26 The tea was a perfect imitation of clover hay. 1901 Daily Colonist (Victoria, B.C.) 1 Nov. 1/5 (Advt.), Clover Hay. Just received several cars of the Choicest Hay for cows. 1847 Emerson Poems, Monadnoc Wks. (Bohn) I. 435 With *cloverheads the swamp adorn. 1830 Tennyson Sea-Fairies, Thick with white bells the *clover-hill swells. 1933 Nat. Geogr. Mag. May 583/1 We thread our way first through the maze of underpasses, overpasses, ‘*clover leaves’ and one-way roads that separates traffic at this busy junction point. 1937 Times 13 Apr. p. viii/1 For straight cross-roads where traffic is heavy and the amount of turning traffic considerable, the ‘clover-leaf’ type of bridge system used both in America and Germany would‥justify the expense. 1939 Archit. Rev. LXXXVI. 58 The clover-leaf junction of Grand Central Parkway and Horace Harding Boulevard. 1951 Amer. Speech XXVI. 207/2 In Nebraska‥a similar intersection‥in which vehicles turn to the right in a nearly complete circle, this to make safely a right angle turn, is termed the cloverleaf. 1957 Listener 26 Sept. 469/1 Their parkways and clover leaves, their elaborate systems of traffic circulation. a1884 Knight Dict. Mech. Suppl., *Clover leaf sight, a rear gun-sight having side lobes, which slightly resemble two foils of the clover leaf. 1796 Hull Advertiser 16 July 1/4 The *clover-ley wheats have‥the advantage of the fallowed. 1805 Forsyth Beauties Scotl. I. 258 To plough down clover ley in a pretty rough state as a most advantageous preparation for wheat. 1807 Vancouver Agric. Devon (1813) 144 Sown after potatoes and the clover-lays. 1888 Elworthy W. Somerset Word-bk., Clover-lay, a field in which there has been a crop of clover, but which is now ready to be ploughed for some other crop. 1856 Farmer's Mag. Jan. 61 *Clover-sheller, with attached dressing apparatus. 1851 H. Stephens Bk. Farm (ed. 2) I. 619/2 Such soils as are termed *clover-sick. 1872 Rep. Vermont Board Agric. 408 The land was what they call ‘clover-sick’. 1894 Country Gentlemen's Catal. 15/2 The latest‥assertion is, that *clover sickness is due to the ravages of‥the eelworm. 1907 Daily Chron. 15 Feb. 4/6 It was intended to make a grant of £300 to Berkhamsted for the investigation of clover sickness. 1933 Discovery Nov. 350/1 The organisms (both fungus and eelworms) which cause ‘clover sickness’. 1867 Mrs. Whitney L. Goldthwaite xi, It was a ‘*clover summer’ for the Josselyns.‥ They must make the most of it.