n. A figure formed of two equilateral triangles placed concentrically with their sides parallel and on opposite sides of the center. This was the seal or symbol of the Pythagorean school.n. In geometry, a figure of six lines.n. In Chinese lit, one of the 64 figures which form the basis of the Yihking or “book of changes,” one of the oldest Chinese books. Each of these figures is made up of six parallel lines, of which some are whole and some divided. See book of changes, under change.