From the second edition (1989):
cocktail, n. and a.
(ˈkɒkteɪl) Also cock-tail. [lit. ‘a tail like that of a cock’, or ‘a tail that cocks up’; the latter is the prevailing notion.]

A. n.

1. a. A cocktailed horse (cf. cock-tailed 1). The fact that hunters and stage-coach horses, the tails of which were generally shortened in this way, were not as a rule thorough-breds seems to have been the origin of the modern turf application. b. ‘Any horse of racing stamp and qualities, but decidedly not thorough-bred, from a known stain in his parentage’ (Dict. Rural Sports 1870, §926).

1808 Ellis Let. 23 Sept. in Lockhart Scott xvii, It is certainly painful to see a race horse in a hackney chaise, but‥the wretched cock tail on whom the same task is usually imposed must, etc. 1842 Thackeray Fitz-Boodle Papers Pref., I can't afford a thorough-bred, and hate a cocktail. 1856 Lever Martins of Cro' M. 221 ‘She's a well-bred one, that's clear.’ ‘Nearly full-bred; the least bit of cocktail in the world.’ 1875 Catal. Sale Sir G. Cholmley's Stud (Tattersall) 1 The half-bred Stock is well enough bred to win Hunters' races and Steeplechases‥being of the best Cocktail strains.

c. transf. A person assuming the position of a gentleman, but deficient in thorough gentlemanly breeding.

1854 Thackeray Newcomes I. 294 Such a selfish, insolent coxcomb as that, such a cocktail. 1887 Academy 11 June 409/2 His cocktails who blunder into liaisons with barmaids.

2. (More fully cocktail beetle): A brachelytrous beetle which ‘cocks up’ the posterior part of the body when irritated; the Devil's Coach-horse.

1880 Antrim & Down Gloss., Coffin-cutter, Ocypus olens, the cock-tail, an insect larger than an earwig, of a black colour. Called also the Devil's Coachman. 1883 Wood in Gd. Words Dec. 762/2 The Rove, or Cocktail Beetles found it out nearly as soon.

3. [A slang name, of which the real origin appears to be lost.] a. A drink, consisting of spirit mixed with a small quantity of bitters, some sugar, etc. orig. U.S.

1806 Balance (Hudson, N.Y.) 13 May 146 Cock tail, then, is a stimulating liquor, composed of spirits of any kind, sugar, water, and bitters. 1809 W. Irving Knickerb. (1861) 241 They lay claim to be the first inventors of those recondite beverages, cock-tail, stone-fence, and sherry-cobbler. 1837 J. E. Alexander Narr. Voy. Colonies W. Africa I. ix. 223 He invited us to take ‘gin sling’, or ‘cock-tail’, at the side-table. 1839 Marryat Diary Amer. Ser. i. III. 288 He frequents the bar, calls for gin cocktails, chews tobacco, and talks politics. 1843 Dickens Mart. Chuz. xvi. 202 He could‥drink more rum-toddy, mint-julep, gin-sling, and cocktail, than any private gentleman of his acquaintance. 1882 J. Hawthorne Fortune's Fool i. xxvii, I would make no more of burglariously entering your premises‥than I would of swallowing a whisky cocktail. 1931 M. de la Roche Finch's Fortune vi. 103 He‥sipped cocktails in the lounge. 1948 New Yorker 6 Nov. 64/2 Cocktails are now so numerous that no bartender‥can remember how to make all of them. 1968 New Society 22 Aug. 266/1 Cocktails, in ‘We're going out to cocktails’, is non-U.

b. Cf. B. 4.

1857 Hughes Tom Brown i. vi. (1878) 121 ‘Bill‥the half-hour hasn't struck. Here, Bill, drink some cocktail.’

c. ellipt. = cocktail party.

1951 N. Mitford Blessing i. viii. 91 If one lunches every day and goes to, say, three cocktails, as well as dining out, one can go to forty houses in a week. 1958 ‘A. Bridge’ Portuguese Escape ii. 20, I must go to a cocktail at the Belgian Embassy.

4. A preparation of food, usu. served as an appetiser at the beginning of a meal; freq. with the main ingredient prefixed, as fruit cocktail, lobster cocktail, prawn cocktail.

1928 Sat. Even. Post 12 May 107/1 Mr. Montgomery had taken a morsel of fruit cocktail. c1938 Fortnum & Mason Catal. 53/1 Oyster Cocktail—per bot. 1/9. 1959 N. Mailer Advts. for Myself (1961) iii. 231 Taking off to greet new arrivals whose crabmeat cocktail she nibbled on. 1960 M. Patten Cookery in Colour no. 23 The correct way of serving these cocktails, though, is to use glasses, when the lettuce should be shredded very finely and put at the bottom of the glasses. Ibid. no. 25 Cocktail sauce for Prawn or Shrimp Cocktail. 1964 Listener 24 Sept. 469/3 Twentieth-century delicacies such as lobster cocktail and coq au vin. 1968 M. Torrie Your Secret Friend iii. 28 What would you think to a nice prawn cocktail, sir?

B. attrib. and adj.

1. That cocks the tail. cocktail beetle: see 2.

1600 Rowlands Let. Humours Blood Epigr. xxxii. 38 How cock-taile proude he doth his head aduance How rare his spurres do ring the moris-daunce. 1866 Athenæum No. 2025. 212/3 Vestiges of cocktail fucoids, coralloids.

2. Of or pertaining to the drink cocktail. attrib. and Comb., as cocktail bar, cocktail cabinet, cocktail glass, cocktail habit, cocktail hour, cocktail lounge, cocktail powder, cocktail table, cocktail time, cocktail tray; cocktail-drinking, cocktail-shaking vbl. ns.; cocktail dress, a dress suitable for wearing at a cocktail party; so cocktail gown, cocktail suit; cocktail-mixer or shaker, a container in which cocktails are vigorously shaken to mix them; cocktail onion, a small pearl onion placed on a stick and served in certain cocktails; cocktail party, a party, esp. one intended for social conversation, at which cocktails are served, usu. together with other alcoholic drinks, savoury snacks, canapés, etc.; cocktail pianist, a player of light inconsequential (usu. jazz-based) background music; so cocktail piano; cocktail sausage, a very small sausage such as is served at cocktail parties; cocktail stick, a small pointed stick on which snacks, sausages, onions, etc., are served at cocktail parties.

1929 E. Sitwell Gold Coast Customs 20 The ghost haunting steamers And *cocktail bars. 1934 W. Plomer Invaders xiv. 262 What the visitors took to be a cocktail bar proved‥to be a gramophone. 1953 E. Smith Guide Eng. Trad. 145 Various‥‘cocktail-bars’ attached to well-known restaurants. 1933 Archit. Rev. LXXIV. 228/2 A *cocktail cabinet. 1958 Times 3 Nov. 14/1 He can afford to buy, on hire purchase, telly, cocktail cabinet, and washing machine. 1935 Times 2 Oct. 17/4 An elaborate dinner ensemble tailored in heavy satin and with a full length skirt‥makes a contrast to the *cocktail dress which retains its skirt about 12 in. from the ground. 1926 D. L. Sayers Clouds of Witness x. 193 I am old-fashioned enough not to have adopted the modern practice of *cocktail-drinking. 1907 E. Wharton Fruit of Tree iii. xxiv. 354 Leaving everywhere in her wake a trail of cigarette ashes and *cocktail glasses. 1930 A. Bennett Imperial Palace xxxi. 208 Cocktail glasses. Yes. Cocktails were the the most profitable trade in the hotel. 1966 G. Greene Comedians i. ii. 53, I remember him raising a cocktail-glass to the light and showing me the delicate engraving of a bull's mask. 1935 Times 25 Nov. 17/5 A dinner or *cocktail gown. 1905 Daily Chron. 22 Dec. 4/5 The *cocktail habit. 1927 Hemingway Men without Women (1928) 68 Sometimes, after the *cocktail hour. 1930 A. Bennett Imperial Palace xiii. 78 ‘Not quite the cocktail hour here, is it?’ said Sir Henry. 1966 Observer (Colour Suppl.) 13 Nov. 40/2 The Cocktail Hour, commonly known as drinks time, is a mysterious 6–8 p.m. limbo. 1939 G. Greene Lawless Roads xi. 287 Racketeers of the brothel and dance-hall and *cocktail lounge. 1904 ‘O. Henry’ Cabbages & Kings iii. 47 A bullet-headed man Smith was, with an oblique, dead eye and the moustache of a *cocktail-mixer. 1951 E. David French Country Cooking 217 Pickled gherkins and baby *cocktail onions. 1928 D. H. Lawrence Lady Chatt. vi. 67 She almost wished she had‥made her life one long *cocktail party and jazz evening. 1950 T. S. Eliot (title) The cocktail party. Ibid. i. i. 12 The only reason for a cocktail party For a gluttonous old woman like me Is a really nice tit-bit. 1962 New Yorker 21 July 68/2 Oscar Peterson (the best *cocktail pianist in the business). 1965 ‘P. Quentin’ Family Skeletons i. 13 But how few people remember cocktail pianists. They're usually considered as part of the furniture. 1952 B. Ulanov Hist. Jazz Amer. (1958) xviii. 230 His *cocktail piano records for Victor insinuate jazz. 1966 Melody Maker 15 Oct. 8/4 This Saturday, he leaves the club as resident pianist and trio leader, and he isn't contemplating a ‘cocktail piano’ job. 1865 Reader 8 July 30 Advertisements of quack medicines, patent skirts, *cock-tail powders, plantation bitters. c1938 Fortnum & Mason Catal. 53/2 Sausages.‥ *Cocktail—per glass 1/3. 1939 Vogue's Cookery Bk. 157, 34 lb. cocktail sausages. 1961 Harrods Food News 5/2 Cocktail Sausages flavoured with chilli. 1868 G. A. Sala in N. & Q. II. 401/1, I never possessed a pair of ‘*cocktail-shakers’ myself, but a young officer in the Blues‥did possess‥a brace of tall silver mugs in which the ingredients of the beverage known as a ‘cocktail’‥are mixed, shaken together, and then scientifically discharged. 1928 Observer 17 June 15/4 A grimacing waiter tilts his cocktail-shaker. 1966 Auden About House 15 Nobody I know would like to be buried with a silver cocktail shaker. 1936 D. Powell Turn, Magic Wheel i. 59 Walter and Corinne‥whispered in the kitchen over the *cocktail-shaking. 1963 Listener 28 Mar. 570/1 Claudel does some improving and cocktail-shaking of the legends. 1937 ‘M. Innes’ Hamlet, Revenge! i. 22 A luridly-tinged cherry speared on a *cocktail-stick. 1953 R. Fuller Second Curtain v. 80 About thirty people stood and talked, holding glasses‥and little sausages on cocktail sticks. 1950 Leader Apr. 1 A slim girl‥in a *cocktail suit. 1965 J. M. Cain Magician's Wife (1966) ii. 18 Flanking it were two sofas, a *cocktail table between. 1929 D. L. Moore Pandora's Let. Box xiii. 242 A *cocktail time dress. 1958 J. Betjeman Coll. Poems 260 Your lives were good and more secure Than ours at cocktail time in Pinner. 1934 N. Marsh Man lay Dead xv. 265 Rankin is bending over the *cocktail tray‥shaking up the last of the cocktail. 1958 M. Stewart Nine Coaches Waiting vi. 73 The entry of Seddon with the cocktail tray interrupted us.

3. Of horses: Not thorough-bred: see A. 1; fig. not in good form, low-bred.

1859 R. E. Egerton-Warburton Hunt. Songs (1883) xl. 113 A hundred good horses, both cocktail and blood. 1875 [see A1]. 1888 Lane-Fox in Pall Mall G. 27 Aug. 9/1 To breed tame fowls and then blow them away from the end of their guns is snobbish and cocktail.

4. Fresh and foaming; said of beer.

1888 Addy Sheffield Gloss., Cock-tail, fresh and foaming. Only applied to beer.