annulus

noun

an·​nu·​lus ˈan-yə-ləs 

plural annuli ˈan-yə-ˌlī 

-(ˌ)lē

also annuluses

1

: ring

2

: a part, structure, or marking resembling a ring: such as

a

: a line of cells around a fern sporangium that ruptures the sporangium by contracting

b

: a growth ring (as on the scale of a fish) that is used in estimating age

Examples of annulus in a Sentence

Recent Examples on the Web

Key Facts Parts of the world will witness a ring of fire annular solar eclipse Wednesday, in which the moon passes between the sun and Earth but does not completely obscure the sun, leaving the sun’s visible outer edge—also called the ring of fire, or annulus—around the moon. —Arianna Johnson, Forbes, 2 Oct. 2024

This results in the sun appearing as a bright ring, or annulus, around the dark silhouette of the moon, according to NASA. —The Arizona Republic, 8 Mar. 2024

On Saturday, the moon will pass in front of the sun, obscuring much of it but leaving behind a brilliant ring, or annulus, of unfiltered sunlight in parts of the western United States. —Matthew Cappucci The Washington Post, Arkansas Online, 9 Oct. 2023

Meanwhile, Matson’s boasts an extremely high level of accuracy in its cementum annuli analysis work. —Katie Hill, Outdoor Life, 28 Sep. 2023

These engagement rings — known as annuli pronubi — may have changed over time, from the simple iron rings described by Pliny to those made of silver and gold. —Sean Mowbray, Discover Magazine, 6 Apr. 2023

Under a low power microscope, a scale with four annuli rings would indicate a four-year period of growth, or a 4-year-old fish. —Jim Gronaw, Baltimore Sun, 19 Mar. 2023

Word History

Etymology

Medieval Latin, from Latin anulus finger ring, from anus ring — more at anus

First Known Use

1563, in the meaning defined at sense 1

Medical Definition

annulus

noun

an·​nu·​lus ˈan-yə-ləs 

variants also anulus

plural annuli -ˌlī  also annuluses

: a ringlike part, structure, or marking

especially : any of various ringlike anatomical parts (as the inguinal ring)