comforter vs pillowslip

comforter

noun
  • A padded cover for a bed, duvet, continental quilt. 

  • A pacifier. 

  • A person who comforts someone who is suffering. 

pillowslip

noun
  • A pillow case. 

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