Also 7 trygon, 7–8 trigone. [ad. L. trigōn-um, ad. Gr. τρίγων-ον triangle, neuter of τρίγωνος, f. τρι-, TRI- + -γων-ος -angled, -cornered.]
1. A figure having three angles and three sides; a triangle.
1600. Fairfax, Tasso, II. li. Let Ismen with his squares and trigons war.
a. 1628. Sir J. Beaumont, Bosworth F., 346. When the Cranes direct their Flight on high,… they in a Trigon fly.
1694. Motteux, Rabelais, IV. Prol. (1737), 78. An equilateral Trigone.
1806. Hutton, Course Math., I. 272. An Equilateral Triangle is also a Regular Figure of three sides … being also called a Trigon.
1859. F. A. Griffiths, Artil. Man. (1862), 333. Trigon … Heptagon … Octagon.
2. Astrol. a. A set of three signs of the zodiac, distant 120° from each other, as if at the angles of an equilateral triangle; TRIPLICITY 3. (Also fig. or allusively.) b. The aspect of two planets distant 120° from each other; = TRINE sb. 2.
1563. [see TRIENT].
1589. Warner, Alb. Eng., VI. xxxi. (1612), 158. She Euen at the firie Trigon shall your chiefe Ascendant be.
1593. G. Harvey, Pierce’s Super., 100. His zeale to God, and the Church, was an aery Triplicity: and his deuotion to his Prince, and the State, a fiery Trigon.
1597. Shaks., 2 Hen. IV., II. iv. 288. Look whether the fierie Trigon his man be not lisping to his master, old tables, his note booke, his counsel keeper?
a. 1633. Austin, Medit. (1635), 7. If the Astronomers hold there was a great Trigon of Constellations at his [Christ’s] Birth: I am sure here is a great Trigon of Trigons, at his Conception.
1644. Lilly, Eng. Proph. Merlin (title-p.), The beginning, and end of the Watry Trygon: An entrance of the fiery Triplicity.
1664. Butler, Hud., II. III. 905. Some … Affirm the Trigons chopp’d and chang’d, The wat’ry with the fiery rang’d.
1704. Hearne, Duct. Hist. (1714), I. 23. Saturn and Jupiter … having run through all the four Trigons, meet again, according to Kepler, at the end of 800 Years.
1819. Jas. Wilson, Compl. Dict. Astrol., s.v. Triplicity, The first trigon is composed of [symbol], [symbol], and [symbol], and is therefore called the fiery triplicity.
3. † a. A triangular instrument used in surveying; also, one used in dialling. Obs.
1590. J. Blagrave, Baculum Familliare (title-p.), A Booke of the making and vse of a Staffe, newly inuented by the Author, called the Familiar Staffe,… which,… staffe … readily performeth all the seuerall vses of the Crosse staffe, the Quadrate, the Circle, the Quadrante, the Gunners Quadrante, the Trigon, [etc.].
1704. J. Harris, Lex. Techn., I. s.v., In Dyaling there is sometimes used an Instrument of a Triangular Form, which is called, a Trigon.
† b. A triangular fort. Obs.
1688. R. Holme, Armoury, III. xvi. (Roxb.), 98/1. A Trigon, a figure of a fort with three corners.
c. An ancient lyre or harp of triangular form.
1727–41. Chambers, Cycl., s.v. The trigon was a kind of triangular lyre, invented by Ibycus.
1776. Hawkins, Hist. Mus., I. II. ix. 247. The Trigon … was … Struck either with a quill, or beaten with little rods.
1879. Stainer, Music of Bible, 11. Attempts to shew that the kinnor was a trigon, or three-cornered harp.
4. Zool. A bivalve of the genus Trigonia.
1835. Kirby, Hab. & Inst. Anim., I. viii. 263. The Trigons, nearly related to the cockle, are mostly fossils.
5. Name of an ancient game at ball (Gr. τρίγων, L. trigōn [‘lusum trigonem,’ Hor., Sat., I. vi. 126]).
1842. W. Smith, Dict. Gr. & Rom. Antiq., 761/2. The most favourite game at ball seems to have been the trigon or pila trigonalis,… played at by three persons, who stood in the form of a triangle.
6. Comp. Anat. The triangle formed by the three cusps of the upper molars in primitive mammals.
1897. H. F. Osborn in Amer. Nat., Dec., 1002. Our studies among the Mesozoic mammals have left no doubt that the upper and lower triangles, or ‘trigon’ and ‘trigonid,’ were derived from the reptilian protocone by the addition of lateral cusps…. The ‘trigon’ was essentially a cutting apparatus, so perfect that many mammals retained it without further evolution.
