Tet"ra*gon (?), n. [L. tetragonum, Gr. tetra`gwnon; te`tra- (see Tetra-) + gwni`a corner, angle: cf. F. tétragone.] 1. (Geom.) A plane figure having four sides and angles; a quadrangle, as a square, a rhombus, etc.
2. (Astrol.) An aspect of two planets with regard to the earth when they are distant from each other ninety degrees, or the fourth of a circle. Hutton.
Te*trag"o*nal (?), a. 1. (Geom.) Of or pertaining to a tetragon; having four angles or sides; thus, the square, the parallelogram, the rhombus, and the trapezium are tetragonal fingers.
2. (Bot.) Having four prominent longitudinal angles.
3. (Crystallog.) Designating, or belonging to, a certain system of crystallization; dimetric. See Tetragonal system, under Crystallization.
||Tet`ra*gram"ma*ton (?), n. [NL., fr. Gr. &?;; te`tra- (see Tetra-) + ||&?; a letter.] The mystic number four, which was often symbolized to ||represent the Deity, whose name was expressed by four letters among ||some ancient nations; as, the Hebrew JeHoVaH, Greek qeo`s, Latin ||deus, etc. || ||Tet`ra*gyn"i*a (?), n. pl. [NL., fr. Gr. te`tra- (see Tetra-) + gynh` ||a woman, female.] (Bot.) A Linnæan order of plants having four styles. || { Tet`ra*gyn"i*an (?), Te*trag"y*nous (?), } a. (Bot.) Belonging to the order Tetragynia; having four styles.
Tet`ra*he"dral (?), a. [See Tetrahedron.] 1. Having, or composed of, four sides.
2. (Crystallog.) (a) Having the form of the regular tetrahedron. (b) Pertaining or related to a tetrahedron, or to the system of hemihedral forms to which the tetrahedron belongs.
Tetrahedral angle (Geom.), a solid angle bounded or inclosed by four plane angles.
Tet`ra*he"dral*ly, adv. In a tetrahedral manner.
Tet`ra*he"drite (?), n. [So called because the crystals of the species are commonly tetrahedrons.] (Min.) A sulphide of antimony and copper, with small quantities of other metals. It is a very common ore of copper, and some varieties yield a considerable presentage of silver. Called also gray copper ore, fahlore, and panabase.
Tet`ra*he"dron (?), n. [Tetra- + Gr. &?; seat, base, fr. &?; to sit.] (Geom.) A solid figure inclosed or bounded by four triangles.
In crystallography, the regular tetrahedron is regarded as the hemihedral form of the regular octahedron.