Symmetry about perpendicular axes.

Geometry and Crystallography. Applied to a solid figure with triangular faces, or having some other relation to a triangle. Also, Having a…

Same as holohedrism n.; opposed to merosymmetry.

a variety of merosymmetry, in which only one fourth of the faces of the holosymmetrical form are retained.

Crystallography. In a crystalline structure: the state of appearing unchanged in orientation following displacement.