/ Dictionary / Index S symmetry element: Meaning and Definition of Find definitions for: sym'metry el"ement Pronunciation: [key] — Crystall. Crystall. 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. symmetry class symmetry plane Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language