Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A polyhedron with four faces.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. a polyhedron with four faces; the regular tetrahedron, the faces of which are equal equilateral triangles, is one of the Platonic solids.

from the GNU version of the Collaborative International Dictionary of English

  • n. A solid figure inclosed or bounded by four triangles.

from The Century Dictionary and Cyclopedia

  • n. A solid comprehended under four plane faces; especially, the regular tetrahedron, or triangular pyramid having its base and sides equilateral triangles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. any polyhedron having four plane faces

Etymologies

Late Greek tetraedron, from Greek, neuter of tetraedros, four-faced : tetra-, tetra- + hedrā, face of a geometric solid.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek τετράεδρον (tetraedron, "triangle-based pyramid"), from τετράς (tetras, "four") + ἕδρα (hedra, "seat"). (Wiktionary)

Examples

  • A tetrahedron is a good model for e.g. a carbon atom in a molecular form, and the tighter the "packing," the tighter the molecular bonds.

    Making Light: The tastemakers of tomorrow

  • Otherwise known as a tetrahedron, a "Caltrop", or to a lesser degree "Ol' Pointy".

    Wherein I am Unmasked

  • Your tetrahedron could be our key to all the mysteries of Omegan science and history.

    Analog Science Fiction and Fact

  • In our space, four equidistant points can be located, the vertices of a tetrahedron, that is, a pyramid having four triangular faces.

    The Fourth Dimension Simply Explained

  • It will be seen that the tetrahedron is the fundamental form, the three-sided pyramid on a triangular base, _i. e._, a solid figure formed from four triangles.

    Occult Chemistry Clairvoyant Observations on the Chemical Elements

  • The tetrahedron is the form of chromium and molybdenum, but not that of the head of their group, oxygen, which is, like hydrogen, _sui generis_.

    Occult Chemistry Clairvoyant Observations on the Chemical Elements

  • Above the tetrahedron is a balloon-shaped figure, apparently drawn into shape by the attraction of the tetrahedron.

    Occult Chemistry Clairvoyant Observations on the Chemical Elements

  • A classic 3D fractal is the Sierpinski tetrahedron, which is a tetrahedron of tetrahedra of tetrahedra, etc.

    MAKE Magazine

  • Through them, one had a spec - tacular view across the river to the futuristic Flamme d'Or, the Phillippe Starke-designed building of black glass, a kind of tetrahedron on acid, surmounted by a vaguely flamelike shape derisively christened by Tokyoites "the Golden Turd."

    Second Skin

  • For the first prize in 1901 the Academy had to consider 20 nominations, but no less than 11 of these named van't Hoff, who was also chosen by the Committee for Chemistry. van't Hoff had already during his thesis work in Utrecht in 1874 published his suggestion that the carbon atom has its four valences directed towards the corners of a regular tetrahedron, a concept which is the very foundation of modern organic chemistry.

    The Nobel Prize in Chemistry: The Development of Modern Chemistry

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