annuluses

Noun

annulus (plural annuluses or annuli)

1. A ring- or donut-shaped area, object, or structure.
   • But by the knots I am ſpeaking of, may it pleaſe your reverences to believe, that I mean good, honeſt, deviliſh tight, hard knots, made bona fide, as Obadiah made his;—in vvhich there is no quibbling proviſion made by the duplication and return of the tvvo ends of the ſtrings through the annulus or...1761, [Laurence Sterne], chapter IX, in The Life and Opinions of Tristram Shandy, Gentleman, volume III, London: […] R[obert] and J[ames] Dodsley […], →OCLC, pages 29–30
2. A ring of fibrous tissue; specifically (cardiology), such a ring around an opening of a heart valve, to which the valve leaflets and muscle fibres of the atria and ventricles are attached; an annulus fibrosus cordis.
3. A ring of light in a celestial body, especially when caused by an annular eclipse (for example, when the Sun and Moon are in line with the Earth, but the Moon does not completely cover the Sun's disc).
4. A structure surrounding a sporangium (or part of it) which shrinks and causes it to rupture for spore dispersal; specifically, in a fern: a structure around about two-thirds of the sporangium consisting of differentially thick-walled cells which dry and distort the sporangium; and in a moss: a complete ring of cells around the tip of the sporangium which dissolves to cause the tip to detach.
5. The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
6. A dark ring on a fish's scale that is formed when a fish's growth rate slows down in the winter due to low food intake and the scale's circuli move closer to one another. The dark ring is used to estimate the fish's age, approximately one year per annulus.

See all 9 meanings of annulus