annulus

[ an-yuh-luhs ]

noun

, plural an·nu·li [an, -y, uh, -lahy], an·nu·lus·es.

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.

annulus

/ ˈænjʊləs /

noun

1. the area between two concentric circles
2. a ring-shaped part, figure, or space

annulus

/ ăn′yə-ləs /

, Plural annuluses ăn′yə-lī′

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.

Word History and Origins

Origin of annulus¹

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

Word History and Origins

Origin of annulus¹

C16: from Latin, variant of ānulus ring

Example Sentences

An “annulus” of bright sunlight rings the moon, but the spectacular corona isn’t visible as it would be during a total eclipse.

From Seattle Times

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

From BBC

Instead it will leave a ring—an annulus—around it as it passes, creating this annular eclipse.

From Scientific American

Shells have always played an important role in Mauritian culture - the Monetaria annulus, commonly known as gold ring cowrie, is a gift of love or luck.

From BBC

The blackberry-like clusters set in the reproductive tiara are sporangia containing many spores, each with a ridged annulus like the bristles on a Roman helmet.

From Scientific American