eiderdown vs pillowcase

eiderdown

noun
  • A quilt stuffed with this down. 

  • The down of the eider duck, used for stuffing pillows and quilts. 

pillowcase

noun
  • A washable, easily removable cloth cover for pillows. 

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