noun a diametral plane.
2. diameter ·noun the length of a straight line through the center of an object from side to side; width; thickness; as, the diameter of a tree or rock.
3. diameter ·noun the distance through the lower part of the shaft of a column, used as a standard measure for all parts of the order. ·see module.
4. diameter ·noun any right line passing through the center of a figure or body, as a circle, conic section, sphere, cube, ·etc., and terminated by the opposite boundaries; a straight line which bisects a system of parallel chords drawn in a curve.