Having a form like or approaching that of a rhomb; having the shape of a rhomboid (see II., 1); rhomboidal.n. In geometry, a quadrilateral figure whose opposite sides and angles are equal, but which is neither equilateral nor equiangular; a non-equilateral oblique parallelogram.n. In crystallography, a solid having a rhomboidal form with three axes of unequal lengths, two of which are at right angles to each other, while the third is so inclined as to be perpendicular to one of the two axes, and oblique to the other.n. In anatomy, a rhomboideus.n. In anthropology, a cranium the norma verticalis of which has a rhomboid form.