Annulus

·noun A ring; a ringlike part or space.

II. Annulus ·noun Ring-shaped structures or markings, found in, or upon, various animals.

III. Annulus ·noun A space contained between the circumferences of two circles, one within the other.

IV. Annulus ·noun The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it.