repr. Gr. τριάκις thrice; used in combination in Geom. and Cryst. in Triakisicosahedron, Triakisoctahedron, Triakistetrahedron (pl. in all cases -hedra), names of solids derived respectively from the icosahedron, octahedron, and tetrahedron by erecting a triangular pyramid on each face, thus multiplying the original number of faces by three. (In Geom. specially applied to those forms in which the pyramids are of such altitude as to make all the solid angles regular.) Hence in derived adjs., as Triakisoctahedrid.
1878. Gurney, Crystallogr., 89. The form … called the triakisoctahedron.
1895. Story-Maskelyne, Crystallogr., vii. § 174. 199. The triakisoctahedron or octahedrid pyramidion … the more acute the pyramidion the more nearly it approximates in aspect to a rhomb-dodecahedron. Ibid., § 187. 220. Triakisoctahedrid forms met with in combination. Ibid., § 189. 224. The triakistetrahedra … (tetrahedrid pyramidia).
