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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.
1794G. Adams Nat. & Exp. Philos. II. xiv. 46 The internal cavity is found to be lined with beautiful tetrahedral prisms. 1812Sir H. Davy Chem. Philos. 124 Four particles may compose a tetrahedron, five a tetraedral pyramid, six an octaedron. 1828Stark Elem. Nat. Hist. II. 139 Body tetraedral, furrowed above. 1878Gurney Crystallogr. 85 The tetrahedral quoins..of the rhombic dodecahedron.
b. Quadrilateral, quadrangular. (Also in comb.)
1816Kirby & 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.
1805–17R. Jameson Char. Min. (ed. 3) 200 Tetrahedral (Haüy tetraèdre), when the crystal has the regular tetrahedron as a secondary form. Example, Tetrahedral blende. 1876Harley Mat. Med. (ed. 6) 369 The spores are minute, tetrahedral granules, each presenting four facets, and are minutely ridged by a hexagonal network. 1903A. 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.
1939W. W. R. Ball Math. Recreations & Ess. (ed. 11) ii. 59 The sums of consecutive triangular numbers are the tetrahedral numbers. 1983Austral. 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.
1860Mayne Expos. Lex., Tetrahedricus,..tetrahedrical. 1864Webster, Tetrahedrally (citing Dana). 1882Vines 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. |