ditrigonal

from The Century Dictionary.

• In crystallography, twice-three-sided. A ditrigonal prism is a six-sided prism, the hemihedral form of a twelve-sided or dihexagonal prism.
• Noting a type of symmetry characterized by a trigonal axis (that is, one of threefold symmetry), in which axis three planes of symmetry intersect. See symmetry.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Being trigonal in two different ways on the same axis; i.e., of a six-sided object, having only the alternate interfacial angles equal