Annulus (&unr_;), n.; pl. Annuli (&unr_;). [L.] 1. A ring; a ringlike part or space.
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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.
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3. (Zoöl.) Ring-shaped structures or markings, found in, or upon, various animals.
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