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
The disk is actually an annulus, like a DVD with a hole in the middle.
—Discover Magazine, 11 Dec. 2011
But at the playa edge, called the annulus, water continues to flow into the aquifer even after the cracks at the bottom seal up.
—John Richard Saylor, Discover Magazine, 18 Apr. 2021
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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
The disk is actually an annulus, like a DVD with a hole in the middle.
—Discover Magazine, 11 Dec. 2011
But at the playa edge, called the annulus, water continues to flow into the aquifer even after the cracks at the bottom seal up.
—John Richard Saylor, Discover Magazine, 18 Apr. 2021
Cite this Entry
“Annulus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/annulus. Accessed 18 Jul. 2025.
Copy CitationMedical Definition
annulus
noun
an·nu·lus
ˈan-yə-ləs
variants
also anulus
plural annuli
-ˌlī
also annuluses
also annuluses
: a ringlike part, structure, or marking
especially
: any of various ringlike anatomical parts (as the inguinal ring)
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