octahedron

IPA: ɑktʌhˈidrʌn

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

Examples of "octahedron" in Sentences

The octahedron can be made from four cards and an icosahedron with ten of them.
The tetrahedron was fire, the cube earth, the octahedron air, the icosahedron water and the dodecahedron the encompassing dome.
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.
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.
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).
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.
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.