annulus

‖n.; pl. Annuli [ L. ] 1. A ring; a ringlike part or space. [ 1913 Webster ]

2. (Geom.) (a) A space contained between the circumferences of two circles, one within the other. (b) The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it. [ 1913 Webster ]

3. (Zool.) Ring-shaped structures or markings, found in, or upon, various animals. [ 1913 Webster ]