The Collaborative International Dictionary of English v.0.48:

Tetrahedral \Tet`ra*he"dral\, a. [See Tetrahedron.]
   1. Having, or composed of, four sides.
      [1913 Webster]

   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.
          [1913 Webster]

   Tetrahedral angle (Geom.), a solid angle bounded or
      inclosed by four plane angles.
      [1913 Webster]