Definitions

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

  • n. A polyhedron having 20 faces.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A polyhedron with twenty faces.
  • n. A regular icosahedron: one of the Platonic solids, all of whose faces are regular triangles

from the GNU version of the Collaborative International Dictionary of English

  • n. A solid bounded by twenty sides or faces.

from The Century Dictionary and Cyclopedia

  • n. A solid bounded by twenty planes.

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

  • n. any polyhedron having twenty plane faces

Etymologies

Greek eikosaedron : eikosi, twenty; + -edron, -hedron.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek εἰκοσάεδρον, from εἴκοσι ("twenty") + ἕδρα (hedra, "face of a geometrical solid"). (Wiktionary)

Examples

  • The icosahedron is another of the five regular, or Platonic, bodies having all their sides, angles, and planes similar and equal.

    Amusements in Mathematics

  • Then, about 10 years ago, the mathematician Reidun Twarock developed a more general theory of the geometry of viruses based on the symmetries of the icosahedron, but using shapes in six dimensions, not three.

    New Angles on Biology

  • I've rolled the icosahedron and painted a few miniatures myself so it only raises my charisma to be accepted by that culture.

    Archive 2009-08-01

  • The company receives more than 1 million applications a year and identifies the top candidates through a rigorous screening process that analyzes SAT scores, grade-point averages and their performance on tests with such questions as: "How many different ways can you color an icosahedron with one of three colors on each face?"

    Google Hiring More Than 6,200 Workers This Year

  • Join five equilateral triangles together and you have the first part of an icosahedron C.

    HERE’S LOOKING AT EUCLID

  • Only five shapes fit the bill: the tetrahedron, the cube, the octahedron, the icosahedron and the dodecahedron, the quintet known as the Platonic solids since Plato wrote about them in the Timaeus.

    HERE’S LOOKING AT EUCLID

  • The octahedron can be made from four cards and an icosahedron with ten of them.

    HERE’S LOOKING AT EUCLID

  • The tetrahedron was fire, the cube earth, the octahedron air, the icosahedron water and the dodecahedron the encompassing dome.

    HERE’S LOOKING AT EUCLID

  • This set of five polyhedra came with the faces already numbered, to make it easy to see that there were 12 sides on a dodacahedron, or 20 on an icosahedron, which made them easy to use as dice.

    The Braunstein Game « Isegoria

  • George Hart has nice pictures including an icosahedron as well.

    The Dodecahedra

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