jack-knife, n.
(ˈdʒæknaɪf)
[app. of U.S. origin: perh. associated with some sense of Jack n.1, but cf. jackleg knife s.v. jockteleg.]
1. A large clasp-knife for the pocket: see also quot. 1867.
| 1711 Official Rec. Springfield, Mass. (1898–9) IX. 39 One Dozen of Jack Knives, at six pence the knife. 1776 Militia Act, New Hampsh. in Outing (1895) XXVII. 80/1 A hundred buckshot, a jack-knife and tow for wadding, six flints, one pound of powder. 1825 J. Neal Bro. Jonathan II. 227 Ever in Jerusalem?—I was—got a jacknife, that..emperor Titus..he lost it, one afternoon. 1861 Dickens Gt. Expect. xl, Taking out his great horn-handled jack-knife..and cutting his food. 1867 Smyth Sailor's Word-bk., Jack-knife, a horn-handled clasp-knife with a laniard, worn by seamen. 1870 Emerson Soc. & Solit., Work & Days Wks. (Bohn) III. 69 The old school-house, and its porch, somewhat hacked by jack-knives. |
2. In a telephone station: = Jack n.1 15 d.
3. Swimming. In full, jack-knife dive. A kind of dive executed by first doubling up and then straightening the body before entering the water.
| 1922 Country Life (U.S.) July 60/3 All variety dives fall into four main groups—somersaults, twists, gainers, jack-knives. 1928 Radio Times 11 May 274/2 Doing jack-knife and swallow dives from incredible heights. 1942 J. D. Carr Seat of Scornful xiv. 191 That's not a jack-knife, you ass... A jack-knife dive is where you bend double and touch your toes in mid-air, and then straighten out before you hit the water. 1956 J. Symons Paper Chase x. 60 His long legs drawn up like those of a jack-knife-diving swimmer. |
4. The accidental folding up of an articulated lorry.
| 1966 Times 29 Sept. 11/6 A ‘jack-knife’ is an ugly complaint of ‘artics’ as these articulated monsters [sc. lorry and trailer] are known familiarly in the trade. The trailer and lorry fold up like a Boy Scout's jack-knife. |
Hence jack-knife v., (a) trans. to cut with a jack-knife; (b) intr. to double up like a jack-knife; spec. of the sections of an articulated lorry: in an accident, to fold together like a jack-knife; (c) to do a jack-knife dive. So ˈjack-knifing vbl. n.
| 1806 Balance (Hudson, N.Y.) 22 July 228 (Th.), A sailor..Jacknifed (as he termed it) the poor creature [sc. a cat] in several places about the head. 1855 Boyd Oakw. Old i, The stage-yankee's method of recording things, in jackknifed notches on a softwood stick. 1888 Century Mag. June 251/2 The practice..of dodging shots, ‘jack-knifing’ under fire. 1889 Amer. Ann. Deaf Oct. 277 Desks ink-stained and jack-knifed like those of a country school. 1897 H. Porter Campaigning w. Grant ix. 141 One of their amusements in camp..was to throw stones and chips past one another's heads, and raise a laugh at the active dodging and bending the body low or ‘jack-knifing’ as the men called it. 1920 T. S. Eliot Ara Vos Prec 22 The sickle motion from the thighs Jackknifes upward at the knees Then straightens down from heel to hip. 1949 Sun (Baltimore) 4 Aug. 1/8 An automobile crashed into a tractor-trailer truck that jackknifed in a driving rain. 1955 T. Sterling Evil of Day v. 50 He..jack-knifed into a chintz armchair. 1958 Times 12 Apr. 7/7 Nobody envies Joe Cree his new ‘artic.’, for there is always the danger that, on ice, the rear will swing round, or jack-knife. 1964 [see fin v. 4]. 1968 New Scientist 14 Mar. 573/3 Jack-knifing accidents to articulated vehicles are all too common... The vehicle folds up—jack-knifes—at the kingpin, which is the hinge between the two parts. 1971 Rand Daily Mail 27 Mar. 8/2 This was particularly so in the case of drivers, where jackknifing of the upper torso onto the steering wheel rim could lead to serious injuries. 1971 New Scientist 12 Aug. 359/2 Commercial vehicles..need them [sc. antilock brakes] most urgently because of their widely varying states of load and their tendency to jack-knife if articulated. |
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Add: 5. Statistics. A versatile method of reducing the bias of estimates and assessing their variability, using subsets of the available data which are often obtained by deleting a single value from the complete set.
| 1964 Ann. Math. Statistics XXXV. 1594 Turkey adopted the name ‘jackknife’ [in 1958] for this procedure, since a boy scout's jackknife is symbolic of a rough-and-ready instrument capable of being utilized in all contingencies and emergencies. 1968 Mosteller & Tukey in Lindzey & Aronson Handbk. Social Psychol. (ed. 2) II. x. 134 The mean of results based on several subsamples is likely to be more biased than is a single result based on all the data, at least to the extent that the individual samples are small. A method with wide application, intended to ameliorate these problems, is the jackknife. 1971 Kendall & Buckland Dict. Statistical Terms (ed. 3) 77/1 ‘Jacknife’ [sic], a method..which reduces bias in estimation and provides approximate confidence intervals in cases where ordinary distribution theory proves difficult. 1983 Sci. Amer. May 107/3 The jackknife proceeds by removing one observation at a time from the original data and recalculating the statistic of interest for each of the resulting truncated data sets. |