delta
(ˈdɛltə)
[Gr. δέλτα (ad. Phœnician daleth), name of the fourth letter of the Greek alphabet; also the land at the mouth of the Nile (Herod.), the Indus (Strabo), etc.]
1. The name of the fourth letter of the Greek alphabet, having the form of a triangle (Δ), and the power of D.
| c 1400 Mandeville (1839) iii. 20 Ȝif ȝee wil wite of here A, B, C..thei clepen hem..α Alpha..δ Deltha..ω Omega. 1601 Holland Pliny I. 96 Many haue called ægypt by the name of the Greeke letter Delta. 1860 T. A. G. Balfour Typ. Char. Nature 118 In Botany the symbol of a perennial plant is a Delta. |
b. An examiner's fourth-class mark (often the lowest grading category). Also
transf., applied to a person.
| 1911 T. H. Warren Oxford & Poetry in 1911 19 Swinburne estimated in superlatives or the opposite. His marks were all α+ or δ-. 1932 A. Huxley Brave New World ii. 24 Why go to the trouble of making it psychologically impossible for Deltas to like flowers? 1958 [see beta 3]. |
2. a. Hist. (
The Delta.) The tract of alluvial land enclosed and traversed by the diverging mouths of the Nile; so called from the triangular figure of the tract enclosed between the two main branches and the coast-line.
| 1555 Eden Decades 250 The goulfe of Arabie..from whense they determyned to brynge a nauigable trench vnto the ryuer of Nilus, where as is the fyrst Delta. 1601 Holland Pliny I. 67 As in ægypt Nilus maketh that which they call Delta. 1636 Sir H. Blount Voy. Levant (1637) 57, I enquired of the Delta, and the Niles seven streames. 1732 T. Lediard Sethos II. ix. 354 The most convenient port of the Delta. 1875 Jowett Plato (ed. 2) III. 529 At the head of the Egyptian Delta, where the river Nile divides. |
b. Geog. The more or less triangular tract of alluvial land formed at the mouth of a river, and enclosed or traversed by its diverging branches.
| 1790 Gibbon Misc. Wks. (1814) III. 453 The triangular island or delta of Mesola, at the mouth of the Po. 1794 Sullivan View Nat. I. 94 The earthy matter, borne down by the floods, is..thrown back upon the shores, into bays and creeks, and into the mouths of rivers, where it forms deltas. 1830 Lyell Princ. Geol. I. 13 Islands have become connected with the main land by the growth of deltas and new deposits. 1836 Marryat Olla Podr. xxvi, The two rivers..enclose a large delta of land. 1893 Nation 16 Feb. 125/1 The villages are situated on small deltas, built by torrential streams that descend from the neighboring hills. |
3. a. Any triangular space or figure;
† the constellation of the Triangle.
| 1638 C. Aleyn Hist. Hen. VII, 134 But if the nobler souls, as they maintein'd, Were fixed in the body of some starre, Then Edwards murder'd sonnes and Warwickes are In those call'd Delta, of Triangle fashion. |
b. Electr. In three-phase electrical equipment, the arrangement of the three windings in series in a manner represented by a triangle, each of the three wires of the circuit being connected to a junction of two windings; chiefly used
attrib., as
delta connection.
| 1902 Encycl. Brit. XXVII. 582/2 Any three-phase winding may be changed over from the star to the delta connection. Ibid. 592/1 If the three coils are closed upon themselves in a mesh or delta fashion. 1943 Gloss. Terms Electr. Engin. (B.S.I.) 19 Delta connection, a method of connection, in three-phase A.C. working, in which three conductors or windings are so connected that they may be represented diagrammatically by a triangle. |
4. attrib. and
Comb., as
delta-formation,
delta-land;
delta connection (see above); hence
delta-connected adj.;
delta frequency,
rhythm,
wave, the most slowly varying of the ‘brain waves’ recorded by an electroencephalograph, having a frequency of less than about three per second and normally present only during deep sleep;
delta-metal, an alloy of copper, zinc, and iron introduced about 1883, and named in allusion to its
three constituents;
delta plain, the flat area of a delta;
delta plateau, a raised delta plain;
delta-rays or
δ-rays, rays of low penetrating power consisting of slow electrons released by the passage of ionizing particles such as alpha-rays through matter;
delta wing, a type of triangular swept-back aeroplane wing; so
delta-winged a., descriptive of aircraft with this type of wing.
| 1964 R. F. Ficchi Electrical Interference x. 201 If it is necessary to establish a neutral with a *delta-connected secondary, grounding transformers are used to form a neutral solidly connected to ground. |
| 1862 Dana Man. Geol. ii. 647 Stratification of *delta deposits. |
| 1858 Geikie Hist. Boulder ix. 172 The process of *delta-formation remains essentially the same, both in lakes and at the sea. |
| 1961 Lancet 16 Sept. 631/1 Low-amplitude slow activity much of it of *delta frequency, compatible with a delirium. |
| 1806 Forsyth Beauties Scotl. IV. 225 The Carse..considered as the finest sort of alluvial or *delta land. |
| 1883 Engineer 23 Feb. 140 Mr. Alexander Dick [has] succeeded in producing an alloy which he calls ‘*Delta metal’. 1884 Times 14 June 8 ‘Delta metal’..is an alloy of copper, zinc, and iron..A steam launch..has..been built entirely of this metal [by Mr. A. Dick]. |
| 1890 W. M. Davis in Bull. Geol. Soc. America I. 200 Glacial Sand Plains... A corollary of the rapid growth of the *delta plains compared to the retreat of the ice is, that the growth of the delta plains was a local..spasmodic operation. |
| 1892 ― in Proc. Boston Soc. Nat. Hist. XXV. 489 Sand plateaus as deltas, marginal to the decaying ice sheet... The size of the delta would depend on the activity of the feeding stream from the ice, and on..the gravel ridges or eskers so often extending backward from the head of the *delta plateau. |
| 1908 Rutherford & Geiger in Proc. R. Soc. A. LXXXI. 163 It is well known that the α-particles, in their passage through matter, liberate a large number of slow-velocity electrons, or *δ-rays, as they have been termed by J. J. Thomson. 1966 McGraw-Hill Encycl. Sci. & Technol. I. 267/2 An appreciable fraction, roughly one-half, of the energy lost by α-rays appears as δ-rays. |
| 1938 Jrnl. Neurol. & Psychiatry I. 383 A similar *delta rhythm appears locally when only a part of the cortex is affected. 1943 Electronic Engin. XV. 520 A waveform of much lower frequency which is characteristic of a cerebral tumour. The name delta rhythm has been given to this wave which usually has a frequency of 3 c/s or lower. |
| 1936 W. Grey Walter in Lancet 8 Aug. 308/1 It is suggested that..these slow waves from the neighbourhood of tumours be called ‘*δ waves’ until their true nature be discovered. 1957 Dorland Med. Dict. (ed. 23) 1540/2 Delta waves, waves in the electroencephalogram which have a frequency of ½ to 3 per second. 1968 Brit. Med. Bull. XXIV. 202/1 The background consists of random slow activity which is symmetrical and there are some delta waves mixed with the alpha rhythm. |
| 1946 Jrnl. Brit. Interplan. Soc. VI. 94 The first effect..can..be reduced but not eliminated by the use of a very low aspect-ratio triangular wing platform (the so-called ‘*Delta’ wing). 1951 Engineering 20 Apr. 474/3 Type of..swept-back ‘delta’-wing experimental aircraft. 1970 Flight (Life Science Libr.) 181 The delta wing of the F-106 Delta Dart..combines the advantages of sweepback with those of a thin wing, and is structurally stronger and easier to build than either. |
| 1950 Nat. Geogr. Mag. Sept. 282/2 Among the latest to be tested against Father Time and the laws of aerodynamics is the new Air Force *delta-winged plane. 1954 Economist 11 Sept. Suppl. 2/1 This year..Gloster Aircraft were able to put five delta-winged Javelins in the air at once. |
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[4.] delta cell Histol., a cell of the islets of Langerhans which produces the hormone somatostatin.
| [1931 W. Bloom in Anatomical Rec. XLIX. 368, I have found three types of granular cells in the islets of Langerhans. One of these is the A type, [etc.]... In some of the D cells, the cytoplasm appears homogeneously blue.] 1942 T. B. Thomas in Anatomical Rec. LXXXII. 334 The *delta cells contain bright blue granules and range in size from small wedge-shaped cells to large rounded ones similar to the beta cells. 1959 W. Andrew Textbk. Compar. Histol. vii. 305 Birds have been shown to have two types of islets in the pancreas... The second is dark and consists of alpha and delta cells along with transitional forms. 1979 Sci. Amer. Nov. 57/3 The delta cells secrete the hormone somatostatin, which inhibits the secretion of both insulin and glucagon. |