annulus

American  

[an-yuh-luhs] / ˈæn yə ləs /

noun

plural

annuli, annuluses

1. a ring; a ringlike part, band, or space.

2. Geometry. the space between two concentric circles on a plane.

3. the veil remnant on a mushroom stalk.

4. a growth ring, as on the cross section of a tree trunk, that can be used to estimate age.

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annulus British  

/ ˈænjʊləs /

noun

1. the area between two concentric circles

2. a ring-shaped part, figure, or space

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annulus Scientific  

/ ăn′yə-ləs /

plural

annuluses

1. A ringlike figure, part, structure, or marking, such as a growth ring on the scale of a fish.

2. A ring or group of specialized cells around the sporangia of many ferns. By changing shape in response to variations in humidity, it breaks open the sporangium and then releases the spores with a whipping motion.

3. The ringlike remains of a membrane (called a veil), found around the stipes of certain basidiomycete mushrooms. The presence or absence of an annulus is often used to identify the species of an individual mushroom.

4. The figure bounded by and containing the area between two concentric circles.

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Etymology

Origin of annulus

1555–65; < Latin, variant of ānulus, equivalent to ān ( us ) ring + -ulus -ule

Example Sentences

It's called an annular eclipse because just a thin ring, or annulus, of light remains visible.

From BBC • Oct. 10, 2023

The circular annulus sector R bounded by the circles 4x2 + 4y2 = 1 and 9x2 + 9y2 = 64, the line x = y 3, and the y-axis is shown in the following figure.

From Textbooks • Mar. 30, 2016

The red primer annulus makes me lean towards Iran, but this example could quite easily have come from either country.

From New York Times • Nov. 7, 2012

Its tubercles and soft tissues were inflamed, and the annulus fibrosus of its disks was the color of bad teeth.

From The New Yorker • Feb. 28, 2011

View of under side showing stem, annulus, gills, and margin of pileus.

From Studies of American Fungi. Mushrooms, Edible, Poisonous, etc. by Atkinson, George Francis