The Collaborative International Dictionary of English v.0.48:

Aigret \Ai"gret\, Aigrette \Ai*grette\, n. [F., a sort of white
   heron, with a tuft of feathers on its head; a tuft of
   feathers; dim. of the same word as heron. See Heron, and
   cf. Egret, Egrette.]
   1. (Zool.) The small white European heron. See Egret.
      [1913 Webster]

   2. A plume or tuft for the head composed of feathers, or of
      gems, etc. --Prescott.
      [1913 Webster]

   3. A tuft like that of the egret. (Bot.) A feathery crown of
      seed; egret; as, the aigrette or down of the dandelion or
      the thistle.
      [1913 Webster]

WordNet (r) 3.0 (2006):

aigrette
    n 1: a long plume (especially one of egret feathers) worn on a
         hat or a piece of jewelry in the shape of a plume [syn:
         aigrette, aigret]