duvet vs kaross

duvet

noun
  • A quilt or usually flat cloth bag with a filling (traditionally down) and usually an additional washable cover, used instead of blankets; often called a comforter or quilt, especially in US English. 

kaross

noun
  • A treated animal-skin cloak or blanket with the hair still left on. 

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