noun (n)

• a toroidal shape(noun.shape)

  Synonym:
  anchor ring, doughnut, halo, ring
  

  source: wordnet30
• (Fungi) a remnant of the partial veil that in mature mushrooms surrounds the stem like a collar(noun.plant)

  Synonym:
  skirt
  

  source: wordnet30
• A ring; a ringlike part or space.(noun)

  source: webster1913