pl. -·li· or -·luses
any ring or ringlike part, mark, etc.
Origin of annulusClassical Latin annulus, for anulus: see annular
nounpl. an·nu·lus·es or an·nu·li
- A ringlike figure, part, structure, or marking, such as a growth ring on the scale of a fish.
- a. A ring or group of thick-walled cells around the sporangia of many ferns that functions in spore release.b. The ringlike remains of a broken partial veil, found around the stipes of certain mushrooms.
- Mathematics The figure bounded by and containing the area between two concentric circles.
Origin of annulusLatin anulus, ring, diminutive of anus.
(plural annuluses or annuli)
- A ring- or donut-shaped area or structure.
- (geometry) The region in a plane between two concentric circles of different radius.
- (topology) Any topological space homeomorphic to the region in a plane between two concentric circles of different radius.
- (astronomy) The ring of the sun not covered by the moon in an annular solar eclipse.
- (botany) Structure in a fern that consists of differentially thick-walled cells on a sporangium that bend and distort as a result of drying.
- (mycology) The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
- (oil and gas production) The space contained between the centre well bore and any external tubing. Sometimes used for separated gas flow.