umbilicus

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. See navel.
2. n. Biology 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.

Century Dictionary and Cyclopedia

1. n. 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. With the absorption of the yolk-bag or the casting off of the navel-string, the umbilicus remains as a characteristic mark or scar. In man it is a little round pit or depression, its center, being hollowed in by the traction of the umbilical vessels inside the belly, as these degenerate into fibrous cords passing to the liver and to the bladder, forming the round ligament of the former and the urachus of the latter viscus.
2. n. 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. Specifically— In conchology, a circular and more or less centric pit or hollow of the body-whorl of a spiral shell; an umbilicated formation. It is well shown in the figure of the snail herewith.
3. n. In botany: [capitalized] An old generic name (A. P. de Candolle, 1801) for the navelwort, Cotyledon Umbilicus.
4. n. The part of a seed by which it is attached to the placenta; the hilum. See cut under hilum.
5. n. A depression or an elevation about the center of a given surface.
6. n. In antiquity, an ornamented or painted ball or boss fastened upon each end of the stick on which manuscripts were rolled.
7. n. 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.
8. n. 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.

Wiktionary

1. n. anatomy navel

GNU Webster's 1913

1. n. (Anat.) 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; the belly button, in humans.
2. n. (Gr. & Rom. Antiq.) An ornamented or painted ball or boss fastened at each end of the stick on which manuscripts were rolled.
3. n. (Bot.) The hilum.
4. n. A depression or opening in the center of the base of many spiral shells.
5. n. Either one of the two apertures in the calamus of a feather.
6. n. obsolete One of the foci of an ellipse, or other curve.
7. n. 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.

WordNet 3.0

1. n. a scar where the umbilical cord was attached