1607 L. Andrewes Serm. II. 217 In the holy tongue, the word which signifieth life is of the dual number.

1706 A. Bedford Temple Musick iv. 75 It ought to be read..in the Dual or Plural Number.

1874 J. Parker Paraclete 400 The great dual law which makes Adam and Eve one humanity, the dry land and the seas one globe.

1655 H. L'Estrange Reign King Charles 7 His Majesty..conducted her to Canterbury, where the marriage was finally completed..From Canterbury his now dual Majesty took coach for White-hall.

1862 Weldon's Register Aug. 3 That in the dual life of man the working faculty should be married to intellectual beauty.

1871 J. Tyndall Fragm. Sci. (1879) II. vi. 79 Truth is often of a dual character.

1886 Pall Mall Gaz. 1 Dec. 3/1 They..proclaimed it as their policy to get rid of this ‘dual ownership’ in the land.

1891 Daily News 15 Apr. 6/4 The skirt was dual, and rather short.

1650 E. Reeve Introd. Greeke Tongue 9 In the second and third duall, and in the second plurall.

1832 S. T. Coleridge Table-talk 7 July It is very natural to have a dual, duality being a conception quite distinct from plurality.

1858 F. M. Müller German Classics p. vii Gothic grammar.. (where we still find a dual in addition to the singular and plural).

?1541 R. Copland Guy de Chauliac's Questyonary Cyrurgyens ii. sig. Fj^v Howe many tethe ought euery persone to haue?.. In some is founde .xxxij .xvj. in euery Jawe. And in other is founde but [x]xviij. That is to wyt, two douales, two quadruples .viij. molares, and two cassalles [L. duo duales: duo quadrupli: et duo canini: et viii. molares et duo caysales].

1875 City of London Chess Mag. 116 The Black Pawn on the K R file is here omitted as superfluous, and the above-mentioned duals entirely eliminated.

1903 Daily Chron. 11 July 8/7 Your problem is dualled by 22 17.

1906 A. C. White Tours de Force p. xxxiii If White is allowed a choice of continuations, such a choice is called a dual, or multiple, continuation. There are two kinds of duals: Absolute duals..and minor duals.

1966 New Statesman 13 May 705/2 That beautiful piece by Sikdar..had to be disqualified because a dual was discovered and couldn't be cured.

1933 Proc. Inst. Municipal & County Engineers 60 iv. 274/2 The intention of such roads was to so design them as to enable them to carry very fast traffic safely. The only method of doing that was by providing dual carriageways with central strips which could be so treated as to make them a delightful amenity.

1957 I. Murdoch Sandcastle viii. 128 A dried-up grass verge separated her from the dual carriageway.

1968 Listener 11 July 38/3 I had a good blub down the first five miles of the dual carriageway.

1884 Illustr. London News 23 Feb. 170/2 The Dual Control…was the proximate cause of our troubles in Egypt.

1913 Captain Sept. 1069/2 Military influence is seen in the two or three-seated machine with dual control.

1914 Aeroplane 15 July 60/2 Even if the ‘Herring Pond’ is crossed previously by a single or dual control machine.

1930 Aberdeen Press & Jrnl. 18 Mar. 7 A Grebe dual-control aeroplane.

1944 H. C. Dent Educ. Act 1944 21 The compromise on the ‘Dual Control’ of schools is one of the outstanding triumphs of the Act.

1959 Which? May 37/2 All lessons should be on a dual-control car.

1930 Daily Tel. 24 July 10/4 The machine was dual-controlled.

1909 Westm. Gaz. 22 July 8/3 Some system of what is known as dual ignition for the modern high-class..motor-car.

1917 A. G. Clark Text Bk. Motor Car Engin. II. 73 Having in view the high efficiency of the modern magneto, it may be accepted that the dual ignition will only be fitted on the more expensive and high-powered cars to facilitate starting up.

1979 Economist 27 Jan. 41/2 American cruise missiles could be put into Europe under dual-key control.

1980 Hansard Commons 17 June 1353 We could have a dual key if we shared in the cost and the ownership of the weapon, but we do not.

1981 Jrnl. Royal United Services Inst. June 5/2 Various systems equipped with US nuclear weapons and operated on a dual-key basis.

1983 Daily Tel. 15 Feb. 2/3 The controversy over ‘dual key’ continued yesterday despite Mr Heseltine's assurance that, without such an arrangement, Britain could still prevent American Cruise missiles being fired from bases in England.

1905 Strand Mag. Apr. 451/2 I feel my dual personality rather puzzling.

1917 A. Waugh Loom of Youth i. ii. 29 In the corps as Officer Commanding..and as a clerk in orders... His dual personality embodied the spirit of ‘the Church Militant’.

1935 B. Russell Relig. & Sci. v. 140 In cases of what is called dual personality..what seems to outside observation to be one person is, subjectively, split into two.

1958 ‘E. Lancaster’ & J. Poling Strangers in my Body iii. 128 This twenty-five-year-old married female patient was referred for psychological examination with diagnosis of dual personality.

1914 Scotsman 8 Oct. 9/1 The number of ‘dual-purpose’ boats, equipped to burn both coal and oil, includes 38 battleships,..and 21 light cruisers.

1925 J. T. Cole in G. F. Finlay Cattle Breeding ii. xxxii. 431 The ‘dual-purpose’ Shorthorn type imported from England in the first half of last century.

1958 Observer 19 Jan. 5/4 Police action against owners of ‘dual purpose’ cars has increased sharply.

1958 Church Times 21 Nov. 1/2 He saw St. John's—at present a dual-purpose hall which is also dual-owned, the sanctuary belonging to the diocese and the hall to the local authority.

1961 Which? Nov. 301/2 A dual standard (sometimes called switchable) set, which operates at present on the 405-line system, but which is already partly converted and might need only a new tuning unit to make it capable of receiving both 405 and 625-line transmissions.

1965 B.B.C. Handbk. 111 A new television studio in Glasgow and a modified one in Bristol are equipped for dual-standard working.

1873 J. Booth Treat. Some New Geom. Methods I. p. xiv As the properties of space are dual, so must the systems of investigation be dual also.

1877 Encycl. Brit. VI. 719/1 Plücker first gave a scientific dual definition of a curve.]

1910 O. Veblen & J. W. Young Projective Geom. I. i. 27 Dual to the class of all planes on a line we have the class of all points on a line, i.e. the line itself.

1910 O. Veblen & J. W. Young Projective Geom. I. i. 29 He should..state both the original and the dual proposition in the ordinary terminology.

1929 Encycl. Brit. XVIII. 573/1 After the principle of duality in the plane has been comprehended it is necessary only to state one of each pair of dual theorems.

1940 J. L. Coolidge Hist. Geom. Methods ii. ii. 145 The whole volume is largely devoted to theorems which are dual to those already developed.

1989 W. Gellert et al. VNR Conc. Encycl. Math. (ed. 2) xxv. 553 To every theorem of projective geometry there is..a dual form, whose proof follows from that of the original theorem.

1989 W. Gellert et al. VNR Conc. Encycl. Math. (ed. 2) xxv. 555 The theorem ‘A point and a line not through it determine exactly one plane’ has the dual form ‘A plane and a line not in it determine exactly one point’.

1947 P. A. M. Dirac Princ. Quantum Mech. (ed. 3) i. 18 Whenever we have a set of vectors in any mathematical theory, we can always set up a second set of vectors, which mathematicians call the dual vectors.

1971 G. Glauberman in M. B. Powell & G. Higman Finite Simple Groups i. 54 The group dual to v is the group v*.

1977 Sci. Amer. Oct. 112/3 He began by transforming the original map into what mathematicians call a dual form: a planar graph in which each vertex of the graph represents a country and each line segment between vertices represents a border.

1979 E. S. Page & L. B. Wilson Introd. Computational Combinatorics iv. 57 The 3-combination (2 6 7) could be represented by the binary number 01100010... If we interchange zeros and ones we have the combination (1 3 4 5 8), sometimes called the dual combination.

1980 A. J. Jones Game Theory iii. 119 Corresponding to any linear program, there is a related linear program called the dual program.

1959 Times 23 Dec. 4/2 Before 1958–59, 20 miles [of the Great North Road] were already dualled and during the year a further 24 miles were completed.

1961 Times 15 Dec. 8 (caption) Trunk road to be dualled in the current programme.

1969 Oxf. Times 18 Apr. 17 (heading) Northern by-pass to be dualled to Banbury Road.