Annulus vs Annular - What's the difference?

As a noun annulus

is a ring- or donut-shaped area or structure.

pertaining to, or having the form of, a ring; forming a ring; ringed; ring-shaped; as, annular fibers; in the shape of an annulus.

(en-noun)

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.

* (topological space) cylinder

* (ring-shaped structure) torus

* annulate * annulation

(-)

Pertaining to, or having the form of, a ring; forming a ring; ringed; ring-shaped; as, annular fibers; in the shape of an annulus.

The capsule in both families is spherical, with a bistratose wall; the outer cell layer usually bears nodular thickenings

Banded or marked with circles.

* annular eclipse * penannular * semiannular