\Tet`ra*he"dral\, a. [See {Tetrahedron}.]
1. Having, or composed of, four sides.
2. (Crystallog.)
   (a) Having the form of the regular tetrahedron.
   (b) Pertaining or related to a tetrahedron, or to the
       system of hemihedral forms to which the tetrahedron
       belongs.
{Tetrahedral angle} (Geom.), a solid angle bounded or
   inclosed by four plane angles.