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

Stonecutters Bridge in Hong Kong, which opened in December 2009, featured giant towers composed of 32 stainless-steel segments wrapped around a concrete annulus.

From MIT Technology Review

That meant the region in which the center would balance was a ring, or annulus.

From FiveThirtyEight

Thus a hot hoosh is preparing in the central vessel side by side with the melting of snow for cocoa or tea in the annulus.

From Project Gutenberg

Mettenius had laid stress upon various characters, but especially on the oblique annulus as distinctive.

From Project Gutenberg

A distinctive feature is the incomplete annulus of the sporangium.

From Project Gutenberg

The sporangia have very short stalks, and are not provided with an annulus at all.

From Project Gutenberg

The rocky annulus which surrounds it is very lofty and precipitous, and at one point reaches a height of 17,300 feet.

From Project Gutenberg