tetrahedral, a.
(tɛtrəˈhiːdrəl, -ˈhɛdrəl)
Also 8–9 tetraedral.
[f. late Gr. τετράεδρος (see tetrahedron) + -al1.]
1. a. Having four sides (in addition to the base or ends); enclosed or contained laterally by four plane surfaces, as a tetrahedral prism or tetrahedral pyramid. tetrahedral angle, tetrahedral quoin, one bounded by four planes meeting at a common apex.
| 1794 G. Adams Nat. & Exp. Philos. II. xiv. 46 The internal cavity is found to be lined with beautiful tetrahedral prisms. 1812 Sir H. Davy Chem. Philos. 124 Four particles may compose a tetrahedron, five a tetraedral pyramid, six an octaedron. 1828 Stark Elem. Nat. Hist. II. 139 Body tetraedral, furrowed above. 1878 Gurney Crystallogr. 85 The tetrahedral quoins..of the rhombic dodecahedron. |
b. Quadrilateral, quadrangular. (Also in comb.)
| 1816 Kirby & Sp. Entomol. xxvii. (1818) II. 491 Cells with regular tetrahedral bottoms. Ibid. 494 The tetrahedral-bottomed transition cells..still preserved their usual shape of hexagonal prisms. |
2. Of or pertaining to a tetrahedron; having the form of a tetrahedron; spec. in Cryst., belonging to a division of the isometric system of which the regular tetrahedron is the characteristic form.
| 1805–17 R. Jameson Char. Min. (ed. 3) 200 Tetrahedral (Haüy tetraèdre), when the crystal has the regular tetrahedron as a secondary form. Example, Tetrahedral blende. 1876 Harley Mat. Med. (ed. 6) 369 The spores are minute, tetrahedral granules, each presenting four facets, and are minutely ridged by a hexagonal network. 1903 A. G. Bell in Nat. Geog. Mag. June 225 The Tetrahedral principle in Kite Structure. When a tetrahedral frame is provided with aero-surfaces of silk or other material..it becomes a tetrahedral kite, or kite having the form of a tetrahedron. |
3. Math. tetrahedral numbers, the series of integers 1, 4, 10, 20,{ddd}, the nth member of which is the sum of the first n triangular numbers.
| 1939 W. W. R. Ball Math. Recreations & Ess. (ed. 11) ii. 59 The sums of consecutive triangular numbers are the tetrahedral numbers. 1983 Austral. Personal Computer IV. v. 103/1 The Tetrahedral Numbers..represent the number of identical spheres that can be stacked in a complete triangular pyramid, or tetrahedron. |
Hence tetraˈhedrally adv., in a tetrahedral manner or form. So tetraˈhedric, tetraˈhedrical adjs., tetrahedral.
| 1860 Mayne Expos. Lex., Tetrahedricus,..tetrahedrical. 1864 Webster, Tetrahedrally (citing Dana). 1882 Vines Sachs' Bot. 13 The four spores or pollen-grains do not lie in one plane but are arranged tetrahedrally, and have moreover a somewhat tetrahedral form. Ibid. 438. 1890 Smithsonian Rep. 367 This latter [double linking] is an immediate consequence of the tetrahedric conception. |