Annulus

環形 /环形

huánxíng

(region in a plane between two concentric circles of different radii)

環空 /环空

huánkōng

(in a well: the space between a pipe or tube and any pipe, tube, casing, or sides of a hole surrounding it)

蕈環 /蕈环

xùnhuán

(remnants of a partial veil which leaves a ring on the stem of a mushroom)