Octahedron

Oc′ta‐he″dron (–drŏn), n. [Gr. οκτἄεδρον, fr. οκτἄεδροσ eight-sided; οκτἀ- (for οκτὤ eight) + ἕδρα seat, base, from ἕζεσθαι to sit.] (Geom.) A solid bounded by eight faces. The regular octahedron is contained by eight equal equilateral triangles.