'annulus' definitions:

Definition of 'annulus'

(from WordNet)
noun
A toroidal shape; "a ring of ships in the harbor"; "a halo of smoke" [syn: ring, halo, annulus, doughnut, anchor ring]
noun
(Fungi) a remnant of the partial veil that in mature mushrooms surrounds the stem like a collar [syn: annulus, skirt]