n. In geometry, an oblique-angled equilateral parallelogram; a quadrilateral figure whose sides are equal, and the opposite sides parallel, but the angles unequal, two being obtuse and two acute.n. In crystallography, a solid bounded by six equal and similar rhombic planes; a rhombohedron.n. In zoology, a pair of semirhombs forming a rhombic figure, as certain plates of cystic crinoids.n. A material circle.