Etymology

A drawing of a transverse section through a heart, showing the annuli (sense 2) or fibrous rings around the valve openings.

An annulus (sense 3) of the Sun seen from Chiba, Japan, during an annular eclipse on 21 May 2012.

The annulus (sense 4.1) on the tip of the sporangium of the bonfire mossCategory:Entries missing English vernacular names of taxa#bonfire%20moss (Funaria hygrometricaCategory:Entries using missing taxonomic name (species)#Funaria%20hygrometrica)

An annulus (sense 4.2) on the stalk of a spectacular rustgillCategory:Entries missing English vernacular names of taxa#spectacular%20rustgill mushroom (Gymnopilus junoniusCategory:Entries using missing taxonomic name (species)#Gymnopilus%20junonius).

A geometric annulus (sense 5.1).

In this diagram of an oil well, drilling fluid is pumped down the drill string (“a column of drill pipe”) (purple) and circulates back up the annulus (sense 6; yellow), which is the space between the drill string and the casing or hole. This transmits the fluid and torque to the drill bit.

Learned borrowing from Medieval LatinCategory:English terms borrowed from Medieval Latin#ANNULUSCategory:English learned borrowings from Medieval Latin#ANNULUSCategory:English terms derived from Medieval Latin#ANNULUS ānnulus, a misspelling of LatinCategory:English terms derived from Latin#ANNULUS ānulus (“ring, especially one worn on a finger”), from ānus (“ring”) (possibly from Proto-Indo-EuropeanCategory:English terms derived from Proto-Indo-European#ANNULUS *h₁eh₂-n-o- (“ring”), from an uncertain root) + -ulus (diminutive suffix).^[1]

The plural form annuli is a learned borrowing from Medieval LatinCategory:English terms borrowed from Medieval Latin#ANNULUSCategory:English learned borrowings from Medieval Latin#ANNULUSCategory:English terms derived from Medieval Latin#ANNULUS ānnulī.

Pronunciation

• Singular:
  • (Received Pronunciation) IPA^(key): /ˈænjʊləs/Category:English 3-syllable words#ANNULUSCategory:English terms with IPA pronunciation#ANNULUS
  • (General American) IPA^(key): /ˈænjələs/Category:English 3-syllable words#ANNULUSCategory:English terms with IPA pronunciation#ANNULUS

  • Audio (US):

    (file)

    Category:English terms with audio pronunciation#ANNULUS
  • Hyphenation: an‧nu‧lus
• Plural (annuli):
  • (Received Pronunciation) IPA^(key): /ˈænjʊlaɪ/, /-li/Category:English 3-syllable words#ANNULUSCategory:English terms with IPA pronunciation#ANNULUS
  • (General American) IPA^(key): /ˈænjəlaɪ/, /-li/Category:English 3-syllable words#ANNULUSCategory:English terms with IPA pronunciation#ANNULUS
  • Hyphenation: an‧nu‧li

Noun

annulus (plural annuluses or annuli)Category:English lemmas#ANNULUSCategory:English nouns#ANNULUSCategory:English countable nouns#ANNULUSCategory:English nouns with irregular plurals#ANNULUSCategory:English entries with incorrect language header#ANNULUSCategory:Pages with entries#ANNULUSCategory:Pages with 2 entries#ANNULUS

2. A ring- or donut-shaped area, object, or structure.

   Hyponym: torus

   • 1761, [Laurence Sterne], chapter IX, in The Life and Opinions of Tristram Shandy, Gentleman, volume III, London: […] R[obert] and J[ames] Dodsley […], →OCLC, pages 29–30:

     But by the knots I am ſpeaking of, may it pleaſe your reverences to believe, that I mean good, honeſt, deviliſh tight, hard knots, made bona fide, as Obadiah made his;—in vvhich there is no quibbling proviſion made by the duplication and return of the tvvo ends of the ſtrings through the annulus or nooſe made by the ſecond implication of them— […]

     Category:English terms with quotations#ANNULUS

4. (anatomyCategory:en:Anatomy#ANNULUS) A ring of fibrous tissue; specifically (cardiologyCategory:en:Cardiology#ANNULUS), 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.
6. (astronomyCategory:en:Astronomy#ANNULUS) 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).
7. (biologyCategory:en:Biology#ANNULUS)
   2. (botanyCategory:en:Botany#ANNULUS) 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.
   4. (mycologyCategory:en:Mycology#ANNULUS) The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
   6. (ichthyologyCategory:en:Ichthyology#ANNULUS) 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.

      Coordinate terms: circulus, focus

8. (mathematicsCategory:en:Mathematics#ANNULUS)
   2. (geometryCategory:en:Geometry#ANNULUS) The region in a plane between two concentric circles of different radii.
   3. (topologyCategory:en:Topology#ANNULUS) Any topological space homeomorphic to the region in a plane between two concentric circles of different radii.

      Synonym: cylinder

10. (technologyCategory:en:Technology#ANNULUS) 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.

      Category:English terms with quotations#ANNULUS

References

Further reading

• annulus (botany) on Wikipedia.Wikipedia
• annulus (mathematics) on Wikipedia.Wikipedia
• annulus (mycology) on Wikipedia.Wikipedia
• annulus (disambiguation) on Wikipedia.Wikipedia

Etymology

From ānus (“ring”) +‎ -ulusCategory:Latin terms suffixed with -ulus#ANNULUS.

Pronunciation

• (Classical Latin) IPA^(key): [ˈaːn.nʊ.ɫʊs]Category:Latin 3-syllable words#ANNULUSCategory:Latin terms with IPA pronunciation#ANNULUS
• (modern Italianate Ecclesiastical) IPA^(key): [ˈan.nu.lus]Category:Latin 3-syllable words#ANNULUSCategory:Latin terms with IPA pronunciation#ANNULUS

Noun

ānnulus m (genitive ānnulī)Category:Latin lemmas#ANNULUSCategory:Latin nouns#ANNULUSCategory:Latin second declension nouns#ANNULUSCategory:Latin masculine nouns in the second declension#ANNULUSCategory:Latin entries with incorrect language header#ANNULUSCategory:Latin masculine nouns#ANNULUSCategory:Pages with entries#ANNULUSCategory:Pages with 2 entries#ANNULUS; second declension

1. alternative form of ānulus

References

• "annulus", in Charles du Fresne du Cange, Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
• “annulus”, in Harry Thurston Peck, editor (1898), Harper’s Dictionary of Classical Antiquities, New York: Harper & Brothers
• “annulus”, in William Smith et al., editor (1890), A Dictionary of Greek and Roman Antiquities, London: William Wayte. G. E. Marindin