any of the seven groups (cubic, hexagonal, rhombohedral
, tetragonal, orthorhombic, monoclinic, and triclinic) of crystals classified
on the basis of the relationships of their crystallographic axes (imaginary
lines of reference
used to describe
the crystal planes)
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.