n. [ NL., from trapezium + Gr. &unr_; seat, base, fr. &unr_; to sit. ] (Crystalloq.) (a) A solid bounded by twenty-four equal and similar trapeziums; a tetragonal trisoctahedron. See the Note under Trisoctahedron. (b) A tetartohedral solid of the hexagonal system, bounded by six trapezoidal planes. The faces of this form are common on quartz crystals. [ 1913 Webster ]