An"nu*lus (#), n.; pl. Annuli (#). [L.]
A ring; a ringlike part or space.
2. Geom. (a)
A space contained between the circumferences of two circles, one within the other.
The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it.
Ring-shaped structures or markings, found in, or upon, various animals.
© Webster 1913.