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. 2. A fine, soft, thick cloth of wool mixed with silk or cotton; a sort of twilled fustian, like moleskin. {Swan's-down cotton}. See {Cotton flannel}, under {Cotton}.