Source : Webster's Revised Unabridged Dictionary (1913)

Octahedron \Oc`ta*he"dron\, n. [Gr.?, fr. ? eight-side; ? (for ?
   eight) + ? seat, base, from ? to sit.] (Geom.)
   A solid bounded by eight faces. The regular octahedron is
   contained by eight equal equilateral triangles.

Source : WordNet®

octahedron
     n : any polyhedron having eight plane faces
     [also: {octahedra} (pl)]