The Collaborative International Dictionary of English v.0.48:

Annulet \An"nu*let\, n. [Dim. of annulus.]
   1. A little ring. --Tennyson.
      [1913 Webster]

   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.
      [1913 Webster]

   3. (Her.) A little circle borne as a charge.
      [1913 Webster]

   4. (Zool.) A narrow circle of some distinct color on a
      surface or round an organ.
      [1913 Webster]

WordNet (r) 3.0 (2006):

annulet
    n 1: (heraldry) a charge in the shape of a circle; "a hollow
         roundel" [syn: annulet, roundel]
    2: molding in the form of a ring; at top of a column [syn:
       annulet, bandelet, bandelette, bandlet, square and
       rabbet]
    3: a small ring