letterhead vs wallcovering

letterhead

noun
  • Paper marked with a letterhead. 

  • A portion of text at the top of a letter, identifying the sender and often giving their address etc., used for formal correspondence. 

wallcovering

noun
  • A covering for a wall, such as wallpaper 

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