noun, plural annuli [an-yuh-lahy] , annuluses.
a ring; a ringlike part, band, or space.
Geometry. the space between two concentric circles on a plane.
the veil remnant on a mushroom stalk. See illus. under mushroom.
a growth ring, as on the cross section of a tree trunk, that can be used to estimate age.

1555–65; < Latin, variant of ānulus, equivalent to ān(us) ring + -ulus -ule Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
annulus (ˈænjʊləs)
n , pl -li, -luses
1.  the area between two concentric circles
2.  a ring-shaped part, figure, or space
[C16: from Latin, variant of ānulus ring]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1560s, medical, from misspelling of L. anulus "little ring."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

annulus an·nu·lus or an·u·lus (ān'yə-ləs)
n. pl. an·nu·lus·es or an·nu·li (-lī')
A circular or ring-shaped structure.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
annulus   (ān'yə-ləs)  Pronunciation Key 
Plural annuluses or annuli (ān'yə-lī')
  1. A ringlike figure, part, structure, or marking, such as a growth ring on the scale of a fish.

  2. A ring or group of specialized cells around the sporangia of many ferns. By changing shape in response to variations in humidity, it breaks open the sporangium and then releases the spores with a whipping motion.

  3. The ringlike remains of a membrane (called a veil), found around the stipes of certain basidiomycete mushrooms. The presence or absence of an annulus is often used to identify the species of an individual mushroom.

  4. The figure bounded by and containing the area between two concentric circles.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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