2. (Gr. & Rom. Antiq.) An ornamented or painted ball or boss
fastened at each end of the stick on which manuscripts
were rolled. --Dr. W. Smith.
4. (Zo["o]l.)
(a) A depression or opening in the center of the base of
many spiral shells.
(b) Either one of the two apertures in the calamus of a
feather.
5. (Geom.)
(a) One of foci of an ellipse, or other curve. [Obs.]
(b) 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}.