sb. (a.). Also 7 -gone. [ad. Gr. τετράγωνον a quadrangle: see TETRA- and -GON. So late L. tetragōn-um, F. tetragone (14th c. in Godef., Compl.).]
1. Geom. A figure having four angles and four sides; a quadrangle considered as one of the polygons. Regular tetragon, a square.
1630. Lennard, trans. Charron’s Wisd. (1658), 22. In figures the Pentagone contains the Tetragone.
1690. Leybourn, Curs. Math., 588. Half the Angle of the Tetragon or Square.
1827. Hutton, Course Math., I. 283. An Equilateral Triangle is also a Regular Figure of three sides, and the Square is one of four: the former being also called a Trigon, and the latter a Tetragon.
2. A square fort; a quadrangular building or block of buildings. Cf. QUADRANGLE sb. 3.
1669. Staynred, Fortification, 1. A Tetragon or Square Fort.
1698. Fryer, Acc. E. India & P., 57. The Fort is a Tetragone from Corner to Corner.
1884. Daily News, 5 Feb., 5/7. Populations living in immense tetragons of brick and stone.
b. A quadrangular court surrounded by buildings or walls, e.g., a college quadrangle.
3. Astrol. The aspect of two planets when they are 90° distant from one another relatively to the earth; the square or quadrate aspect.
a. 1626. Bp. Andrewes, Serm. (1856), I. 185. In the horoscope of Christ’s nativity…. Whether a trigon or no, this tetragon I am sure there was.
1727–41. Chambers, Cycl., Tetragon,… an aspect of two planets with regard to the earth, when they are distant from each other a fourth part of a circle, or 90°…. The tetragon is expressed by the character [char.].
[1819. J. Wilson, Compl. Dict. Astrol., Tetragonus.]
B. adj. Four-cornered, tetragonal, quadrangular.
1794. Morse, Amer. Geog., 553. The remains of an ancient … fortification: it is now a regular tetragon terrace, about four feet high, with bastions at each angle.
