letterhead vs writing paper

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. 

writing paper

noun
  • Paper designed to be written on with ink; it may be ruled or unruled. 

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