(Arch.) A small, flat fillet, encircling a column, etc., used by itself, or with other moldings. It is used, several times repeated, under the Doric capital.
3.
(Her.) A little circle borne as a charge.
4.
(Zool.) A narrow circle of some distinct color on a surface or round an organ.
... a principal bearing is not expressed, it is always understood to occupy the centre of the field. Ex. See Azure, an annulet argent, ... — The Manual of Heraldry; Fifth Edition • Anonymous