covers vs duvet

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. 

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. 

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