\Hem`i*he"dral\, a. [Hemi- + Gr. ? seat, base, fr. ?
to sit.] (Crystallog.)
Having half of the similar parts of a crystals, instead of
all; consisting of half the planes which full symmetry would
require, as when a cube has planes only on half of its eight
solid angles, or one plane out of a pair on each of its
edges; or as in the case of a tetrahedron, which is
hemihedral to an octahedron, it being contained under four of
the planes of an octahedron. -- {Hem`i*he"dral*ly}, adv.