covers vs eiderdown

covers

noun
  • The bedclothes; collectively, the sheets, blankets, etc. 

  • The tarpaulins or other devices used to cover the wicket during rain, in order to prevent it getting wet. 

  • The area of the field near cover and extra cover. 

eiderdown

noun
  • A quilt stuffed with this down. 

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

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