A ring- or donut-shaped area or structure.
The ring of the sun not covered by the moon in an annular solar eclipse.
Structure in a fern that consists of differentially thick-walled cells on a sporangium that bend and distort as a result of drying.
The region in a plane between two concentric circles of different radii.
The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
The space contained between the centre well bore and any external tubing. Sometimes used for separated gas flow.
Any topological space homeomorphic to the region in a plane between two concentric circles of different radius.
A thin, flat, circular plate or similar object.
A disc - either a CD-ROM, an audio CD, a DVD or similar removable storage medium.
A ring- or cup-shaped enlargement of the flower receptacle or ovary that bears nectar or, less commonly, the stamens.
Something resembling a disk.
A type of harrow.
An intervertebral disc
To harrow.
To move towards, or operate at, zero blade pitch, orienting the propeller blades face-on to the oncoming airstream and maximising the drag generated by the propeller.