the depression, or mark, in the median line of the abdomen, which indicates the point where the umbilical cord separated from the fetus; the navel.-an ornamented or painted ball or boss fastened at each end of the stick on which manuscripts were rolled.-the hilum.-a depression or opening in the center of the base of many spiral shells.-either one of the two apertures in the calamus of a feather.-one of foci of an ellipse, or other curve.-a point of a surface at which the curvatures of the normal sections are all equal to each other. a sphere may be osculatory to the surface in every direction at an umbilicus. called also umbilic.