annulus - Wiktionary, the free dictionary (original) (raw)

From Wiktionary, the free dictionary

Learned borrowing from Medieval Latin ānnulus, a misspelling of Latin ānulus (“ring, especially one worn on a finger”), from ānus (“ring”) (from Proto-Indo-European *h₁eh₂no- (“ring”)) + -ulus (diminutive suffix).[1]

The plural form annuli is a learned borrowing from Medieval Latin ānnulī.

annulus (plural annuluses or annuli)

  1. A ring- or donut-shaped area or structure.
    Hyponym: torus
  2. (anatomy) A ring of fibrous tissue; specifically (cardiology), such a ring around an opening of a heart valve, to which the valve leaflets and muscle fibres of the atria and ventricles are attached; an annulus fibrosus cordis.
  3. (astronomy) A ring of light in a celestial body, especially when caused by an annular eclipse (for example, when the Sun and Moon are in line with the Earth, but the Moon does not completely cover the Sun's disc).
  4. (biology)
    1. (botany) A structure surrounding a sporangium (or part of it) which shrinks and causes it to rupture for spore dispersal; specifically, in a fern: a structure around about two-thirds of the sporangium consisting of differentially thick-walled cells which dry and distort the sporangium; and in a moss: a complete ring of cells around the tip of the sporangium which dissolves to cause the tip to detach.
    2. (mycology) The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
    3. (ichthyology) A dark ring on a fish's scale that is formed when a fish's growth rate slows down in the winter due to low food intake and the scale's circuli move closer to one another. The dark ring is used to estimate the fish's age, approximately one year per annulus.
  5. (mathematics)
    1. (geometry) The region in a plane between two concentric circles of different radii.
    2. (topology) Any topological space homeomorphic to the region in a plane between two concentric circles of different radii.
      Synonym: cylinder
  6. (technology) In a well such as an oil well or water well: the space between a pipe or tube and any pipe, tube, casing, or sides of a hole surrounding it.
    • 1950 September, “Notes and News: Pneumatic Buffer Stop, E.R.”, in The Railway Magazine, London: Tothill Press, →ISSN, →OCLC, page 642:
      Pressure balance is obtained by the air pressure in the cylinder operating on a supplementary piston in the buffer piston head, transmitting pressure to a small quantity of oil which is ported to an annulus between the buffer piston seals and the cylinder wall, so that the seal is always under opposing pressures; oil on one side and air on the other.

ring- or donut-shaped area or structure

ring of fibrous tissue; specifically, such a ring around an opening of a heart valve

ring of light in a celestial body, especially when caused by an annular eclipse

structure surrounding a sporangium (or part of it) which shrinks and causes it to rupture for seed dispersal

region in a plane between two concentric circles of different radii

topological space homeomorphic to the region in a plane between two concentric circles of different radii

in a well: the space between a pipe or tube and any pipe, tube, casing, or sides of a hole surrounding it

  1. ^ Compare “annulus, n.”, in OED Online Paid subscription required⁠, Oxford: Oxford University Press, September 2023; “annulus, n.”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.

From ānus (“ring”) +‎ -ulus.

ānnulus m (genitive ānnulī); second declension

  1. Alternative form of ānulus

Second-declension noun.