How do you spell Annulus

Available Definitions:
1)  n. - A ring; a ringlike part or space.
2)  n. - A space contained between the circumferences of two circles, one within the other.
3)  n. - The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it.
4)  n. - Ring-shaped structures or markings, found in, or upon, various animals.