Noun
A solid bounded by eight faces. The regular octahedron is contained by eight equal equilateral triangles.
Source: Webster's dictionaryCorrespondingly, a regular octahedron is the result of cutting off from a regular tetrahedron, four regular tetrahedra of half the linear size (i.e. rectifying the tetrahedron). Source: Internet
Air is made of the octahedron; its minuscule components are so smooth that one can barely feel it. Source: Internet
For example, one can divide an octahedron into four identical tetrahedra and combine them again with two regular ones. Source: Internet
Cartesian coordinates An octahedron with edge length 2 can be placed with its center at the origin and its vertices on the coordinate axes; the Cartesian coordinates of the vertices are then : ( ±1, 0, 0 ); : ( 0, ±1, 0 ); : ( 0, 0, ±1 ). Source: Internet
Earth was associated with the cube, air with the octahedron, water with the icosahedron, and fire with the tetrahedron. Source: Internet
Eight of these irregular octahedra can be attached to the triangular faces of a regular octahedron to obtain the cuboctahedron. Source: Internet