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annulus noun

  /-li/ , /ˈænjəlaɪ/ , /ˈænjələs/ , /ˈænjʊlaɪ/ , /ˈænjʊləs/
  • A ring- or donut-shaped area or structure.
 anello
  • (botany) 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.
  • (geometry) The region in a plane between two concentric circles of different radii.
  • (topology) Any topological space homeomorphic to the region in a plane between two concentric circles of different radii.
 anello, corona circolare
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