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
Example Sentences
Recent Examples on the Web The spores sit inside a sturdy hoop of 12-14 cells that is called the annulus. 
Helen Czerski, WSJ, 25 June 2021 That force comes from the last bits of water inside the annulus cells. Helen Czerski, WSJ, 25 June 2021 That means instead of a total eclipse of the sun, viewers will witness an annular eclipse: the smaller shadow of the moon will blot out less of the sun, and the sun will shine in a brilliant ring of light (an annulus) around the darkness. BostonGlobe.com, 8 June 2021 An annulus, or dark ring, is formed each winter between the cementum formed in spring and summer growth periods. Alan Clemons, Outdoor Life, 18 Mar. 2021 They are easily identified by the red-brown cap fading to tan, white to lilac-gray gills, firm texture, and annulus (ring) around the stout stipe (stalk). Sunset, 22 Jan. 2018 Our last partial eclipse was Oct 23, 2014; the biggest one in recent memory is the May 10, 1994 annular eclipse (annular as in annulus = ring). Dawn Mitchell, Indianapolis Star, 18 Aug. 2017 Instead, for a few minutes the sun looks like a striking annulus, or ring, which is why an annular eclipse is also often called a ring of fire. Andrew Fazekas, National Geographic, 31 Aug. 2016 See More
Helen Czerski, WSJ, 25 June 2021 That force comes from the last bits of water inside the annulus cells. Helen Czerski, WSJ, 25 June 2021 That means instead of a total eclipse of the sun, viewers will witness an annular eclipse: the smaller shadow of the moon will blot out less of the sun, and the sun will shine in a brilliant ring of light (an annulus) around the darkness. BostonGlobe.com, 8 June 2021 An annulus, or dark ring, is formed each winter between the cementum formed in spring and summer growth periods. Alan Clemons, Outdoor Life, 18 Mar. 2021 They are easily identified by the red-brown cap fading to tan, white to lilac-gray gills, firm texture, and annulus (ring) around the stout stipe (stalk). Sunset, 22 Jan. 2018 Our last partial eclipse was Oct 23, 2014; the biggest one in recent memory is the May 10, 1994 annular eclipse (annular as in annulus = ring). Dawn Mitchell, Indianapolis Star, 18 Aug. 2017 Instead, for a few minutes the sun looks like a striking annulus, or ring, which is why an annular eclipse is also often called a ring of fire. Andrew Fazekas, National Geographic, 31 Aug. 2016 See More 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
also annuluses : a ringlike part, structure, or marking
especially : any of various ringlike anatomical parts (as the inguinal ring)