Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A polyhedron with eight faces.

from The Century Dictionary.

  • noun A solid bounded by eight faces.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Geom.) A solid bounded by eight faces. The regular octahedron is contained by eight equal equilateral triangles.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun geometry a polyhedron with eight faces; the regular octahedron has regular triangles as faces and is one of the Platonic solids.

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

  • noun any polyhedron having eight plane faces

Etymologies

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

[Greek oktaedron, from neuter of oktaedros, having eight sides : okta-, octo- + -edros, sided; see –hedron.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Ancient Greek ὀκτώ (oktō, "eight") + ἕδρα (hedra, "seat").

Examples

  • A pyramid is not a Platonic solid because not all the sides are the same, but by sticking an inverted pyramid on the bottom you get an octahedron, which is.

    HERE’S LOOKING AT EUCLID

  • A pyramid is not a Platonic solid because not all the sides are the same, but by sticking an inverted pyramid on the bottom you get an octahedron, which is.

    HERE’S LOOKING AT EUCLID

  • A pyramid is not a Platonic solid because not all the sides are the same, but by sticking an inverted pyramid on the bottom you get an octahedron, which is.

    HERE’S LOOKING AT EUCLID

  • Each "cigar" has a leaf-like body at its base, and in the centre of the octahedron is a globe containing four atoms, each within its own wall; these lie on the dividing lines of the faces, and each holds a pair of the funnels together.

    Occult Chemistry Clairvoyant Observations on the Chemical Elements

  • It is more interesting to me, for instance, to try and find out why the red oxide of copper, usually crystallizing in cubes or octahedrons, makes itself exquisitely, out of its cubes, into this red silk in one particular Cornish mine, than what are the absolutely necessary angles of the octahedron, which is its common form.

    The Ethics of the Dust

  • Unfortunately, analysis of the finite subgroups of SO (3) isn't so easy, and I don't know any easy way of showing why there should only be the five (or four, actually - symmetries of the cube and the octahedron are the same).

    Citizendium, the Citizens' Compendium - Recent changes [en]

  • 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 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

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