The Collaborative International Dictionary of English v.0.48:

Swan's-down \Swan's"-down`\, or Swans-down \Swans"-down`\, n.
   1. The down, or fine, soft feathers, of the swan, used on
      various articles of dress.
      [1913 Webster]

   2. A fine, soft, thick cloth of wool mixed with silk or
      cotton; a sort of twilled fustian, like moleskin.
      [1913 Webster]

   Swan's-down cotton. See Cotton flannel, under Cotton.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "swansdown":
   blubber, breeze, butter, clay, cushion, dough, down, eiderdown,
   feather bed, feathers, fleece, floss, flue, fluff, foam, fur, fuzz,
   kapok, lint, pile, pillow, plush, pudding, puff, putty, rubber,
   satin, silk, thistledown, velvet, wax, wool, zephyr