from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Exhibiting only half the faces required for complete symmetry. Used of a crystal.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Having only half the plane faces needed for the highest degree of symmetry in its system

from the GNU version of the Collaborative International Dictionary of English

  • adj. Having half of the similar parts of a crystals, instead of all; consisting of half the planes which full symmetry would require, as when a cube has planes only on half of its eight solid angles, or one plane out of a pair on each of its edges; or as in the case of a tetrahedron, which is hemihedral to an octahedron, it being contained under four of the planes of an octahedron.

from The Century Dictionary and Cyclopedia

  • In mineralogy, exhibiting hemihedrism; having, as a crystal, only half the number of planes belonging to any particular form which the law of symmetry requires.
  • In mathematics, substituting negative for positive signs in regular alternation.
  • Also hemihedric, hemiedric.
  • In the relation of so-called hemihedral crystals to crystal symmetry, see symmetry.


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