Definify.com
Webster 1913 Edition
Annulus
‖
An′nu-lus
,Noun.
pl.
Annuli
. [L.]
1.
A ring; a ringlike part or space.
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.
3.
(Zool.)
Ring-shaped structures or markings, found in, or upon, various animals.