(ˈ)dī+ noun
Etymology: di- + pyramid
: a crystal consisting of two pyramids base to base, the one geometrically a mirror image of the other with respect to the horizontal plane of symmetry
dipyramids occur in the tetragonal, hexagonal, and orthorhombic systems and may have corresponding orthorhombic, tetragonal, ditetragonal, hexagonal, or dihexagonal symmetry