HEMIHEDRAL
Etymology
Adjective
hemihedral (not comparable)
(of a crystal) Having only half the plane faces needed for the highest degree of symmetry in its system
Source: Wiktionary
Hem`i*he"dral, a. Etym: [Hemi- + Gr. (Crystallog.)
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition