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.