from The Century Dictionary and Cyclopedia

  • In crystallography: Twice four-angled or twice four-sided: said of the eight-faced prism and eight-faced pyramid (or double pyramid) of the tetragonal system.
  • Noting a type of symmetry characterized by a tetrad axis (that is, one of tetragonal or fourfold symmetry) in which four planes of symmetry intersect. See symmetry.


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