umbilicus

A small opening or depression similar to a navel, as the hollow at the base of the shell of some gastropod mollusks, one of the openings in the shaft of a feather, or the hilum of a seed.

In anatomy and zoology, the more or less nearly central point in the walls of the abdomen where the yolk-bag or umbilical vesicle of the embryo hangs, or where the navel-string or umbilical cord enters the belly; the navel; the omphalos.

Hence Some navel-like formation; some circumscribed depression or elevation; a sort of button, or a place in which a button might fit: when elevated instead of depressed, oftener called umbo.

In botany: [capitalized] An old generic name (A. P. de Candolle, 1801) for the navelwort, Cotyledon Umbilicus.

The part of a seed by which it is attached to the placenta; the hilum. See cut under hilum.

A depression or an elevation about the center of a given surface.

In antiquity, an ornamented or painted ball or boss fastened upon each end of the stick on which manuscripts were rolled.

In geometry, a term used by the older geometers as synonymous with focus; in modern works, a point in a surface through which all lines of curvature pass.

The raised central boss of a large plateau or dish, often made to fit the hollow foot of the ewer which stands upon it and forms one design with the dish.