umbilicus

(ŭm-bĭlˈĭ-kəs, ŭmˌbə-līˈkəs)

1. See navel.
2. 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.