Meaning of symmetry element

sym'metry el"ement

Pronunciation: [key]
— Crystall. Crystall.
  1. any of four points, lines, or planes of a crystal: a center of symmetry, a reflection plane, a rotation axis, or a rotation-inversion axis.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.