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

During the rare event, the moon will cover 96% of the sun, leaving a glowing annulus in the sky for up to 2 minutes 20 seconds. — Jamie Carter, Forbes.com, 23 Jan. 2026

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)