annulus

n. ring; ring-like object

Annulus (or anulus), being the Latin for "ring", is a term used to describe various ring-shaped objects:Annulus (entomology), an antennal unit in simple antennae, or a ring-like marking or structure surrounding a joint or segmentAnnulus (anatomy) refers to several structures in human anatomy. The spelling "anulus" is preferred under Terminologia Anatomica, but both spellings are commonly found. Examples include:Annulus fibrosus cordis, the ring-like structure on a heart valve where the valve leaflets are anchoredAnnulus fibrosus disci intervertebralis, the outer wall of the invertebral discAnnulus femoralisAnnulus inguinalis superficialisAnnulus inguinalis profundusAnnulus tendineus communisAnnulus (ichthyology), the annual rings that form in fish scales or bone sectionsAnnulus (mycology), the "ring" on a mushroom stemAnnulus (astronomy), the ring of light from the visible part of the photosphere seen at the greatest extent of an annular eclipseAnnulus (cosmology), the ring around the lens on which strong gravitationally lensed images of one source appearAnnulus (mathematics), a ring-shaped geometric figureAnnulus (firestop), the space in a penetration seal surrounding a penetrant, i.e. between a pipe or electrical conduit, or cable and a sleeve, with or without a firestopAnnulus (oil well), the tube shaped void between the drill string and the formation when drilling an oil wellAnnulus (microscopy), a circular opening "disk" below a specimen slide, required for Phase Contrast microscopyAnnular hurricane, a hurricane that is nearly symmetrical and takes longer to weaken than normal hurricanes.
See more at Wikipedia.org...

Noun
1. a toroidal shape; "a ring of ships in the harbor"; "a halo of smoke"
(synonym) ring, halo, anulus, doughnut, anchor ring
(hypernym) toroid
(hyponym) fairy ring, fairy circle
2. (Fungi) remnant of the partial veil that in mature mushrooms surrounds the lower part of the stem
(hypernym) plant part, plant structure
(part-holonym) partial veil, velum
(classification) Fungi, kingdom Fungi, fungus kingdom

n. annulus, ring; ring-like object

(n.)
The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it.
  

(n.)
Ring-shaped structures or markings, found in, or upon, various animals.
  

(n.)
A space contained between the circumferences of two circles, one within the other.
  

(n.)
A ring; a ringlike part or space.