triakis-|ˈtraɪəkɪs|repr.Gr. τριάκις thrice; used in combination in Geom. and Cryst. in ˌtriakisˌicosaˈhedron, ˌtriakisˌoctaˈhedron, ˌtriakisˌtetraˈhedron (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 ˌtriakisˌoctaˈhedrid.1878Gurney Crystallogr. 89 The form..called the triakisoctahedron.1895Story-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).