a. (sb.) Also (in sense 4) -el. [f. prec. + -AL. So mod.F. tétragonal.]
1. Of or pertaining to a tetragon; having four angles; quadrangular.
1571. Digges, Pantom., IV. T j b. When any equiangle triangle, square, or Pentagonum is … described within a circle,… their sides are called the trigonall, tetragonall and pentagonall Cordes of that circle.
1667. Phil. Trans., II. 627. Two Tetragonal Prismes of Tendons.
1874. Coues, Birds N. W., 592. An elongated pyramid with a tetragonal base.
2. Bot. and Zool. Quadrangular in section, like a ‘square’ rod; tetraquetrous.
1753. Chambers, Cycl. Supp., s.v. Leaf, A leaf that has, instead of three ribs or edges, four or five, is … called tetragonal, pentagonal, &c.
1853. Royle, Mat. Med. (ed. 2), 641. Norway Spruce Fir. Leaves scattered, tetragonal.
1875. C. C. Blake, Zool., 109. The bill is elongate,… tetragonal, and acuminate.
1646. Sir T. Browne, Pseud. Ep., IV. xii. 213. Reckoning on unto the seventh day, the Moone will be in a Tetragonall or Quadrate aspect, that is, 4. signes removed from that wherein the disease began.
4. Her. Represented as quadrangular: see quot.
c. 1828. Berry, Encycl. Her., I. Gloss., Tetragonel Pyramids, piles are generally considered to represent wedges,… they are sometimes borne … square, in which latter case they may be termed square piles, or tetragonel pyramids reversed.
1889. Elvin, Dict. Her., Tetragonal Pyramids.
5. Cryst. Applied to a system of crystallization in which the three axes are at right angles, the two lateral axes being equal, and the vertical of a different length.
1868. Dana, Min. (ed. 5), Introd. 21. Crystallography … systems of crystallization…. Having only the lateral equal. The Tetragonal and Hexagonal.
1878. Gurney, Crystallogr., 38. If four symmetral planes only intersect in the same straight line it is called an axis of tetragonal symmetry.
1879. Rutley, Stud. Rocks, ix. 77. Crystals belonging to the tetragonal and hexagonal systems are singly refractive when viewed in the direction of the principal crystallographic axis.
† B. sb. = TETRAGON 1. Obs. rare–1.
1684. trans. Agrippa’s Van. Arts, To Rdr. The intricate Geometrician will imprison me in his Triangles and Tetragonals.
Hence Tetragonally adv., in a tetragonal manner or form; Tetragonalness.
1727. Bailey, vol. II., Tetragonalness, the having four Corners, Squareness.
1888. Cassell’s Encycl. Dict., Tetragonally.
