noun
: a simple axis of symmetry in a crystal about which the whole crystal configuration is brought into coincidence with its original aspect by a rotation of one half, one third, one fourth, or one sixth of a turn about the axis
noun
: a simple axis of symmetry in a crystal about which the whole crystal configuration is brought into coincidence with its original aspect by a rotation of one half, one third, one fourth, or one sixth of a turn about the axis
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012