Tet`ra*he"dron (?), n. [Tetra- + Gr. seat, base, fr. to sit.] Geom.
A solid figure inclosed or bounded by four triangles.
In crystallography, the regular tetrahedron is regarded as the hemihedral form of the regular octahedron.
Regular tetrahedron Geom., a solid bounded by four equal equilateral triangles; one of the five regular solids.
© Webster 1913.