n. Titanium dioxid, crystallizing in the tetragonal system, the fundamental and commonly occurring form being an acute square octahedron (whence the name); anatase.n. A meteoric iron with octahedral structure, which is usually distinctly marked by the lamellæ of kamacite, tænite, and plessite, seen in the Widmannstättian figures. Most iron meteorites fall in this class. See meteorite.