Annulet

n.
  1. A little ring.
  2. (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. (Zoöl.) A narrow circle of some distinct color on a surface or round an organ.