an·​nu·​lus | \ ˈan-yə-ləs How to pronounce annulus (audio) \
plural annuli\ ˈan-​yə-​ˌlī How to pronounce annulus (audio) , -​(ˌ)lē \ also annuluses

Definition of annulus

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 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, "How to Grow Mushrooms," 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, "Retro Eclipse: When day turned to night and back again," 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, "‘Ring of Fire’ Solar Eclipse This Week: How to See It," 31 Aug. 2016

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'annulus.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of annulus

1563, in the meaning defined at sense 1

History and Etymology for annulus

Medieval Latin, from Latin anulus finger ring, from anus ring — more at anus

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Time Traveler for annulus

Time Traveler

The first known use of annulus was in 1563

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Cite this Entry

“Annulus.” Dictionary, Merriam-Webster, Accessed 20 Jan. 2021.

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More Definitions for annulus


an·​nu·​lus | \ ˈan-yə-ləs How to pronounce annulus (audio) \
variants: also anulus
plural annuli\ -​ˌlī How to pronounce annulus (audio) \ also annuluses

Medical Definition of annulus

: a ringlike part, structure, or marking especially : any of various ringlike anatomical parts (as the inguinal ring)

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