egret vs thistledown

egret

noun
  • The flying feathery or hairy crown of seeds or achenes, such as the down of the thistle. 

  • A plume or tuft of feathers worn as a part of a headdress, or anything imitating such an ornament. 

  • Any of various wading birds of the genera Egretta or Ardea that includes herons, many of which are white or buff, and several of which develop fine plumes during the breeding season. 

thistledown

noun
  • The soft, feathery pappus attached to the seeds of a thistle. 

How often have the words egret and thistledown occurred in a corpus of books? (source: Google Ngram Viewer )