essay vs letterhead

essay

noun
  • A proposed design for a postage stamp or a banknote. 

  • A written composition of moderate length, exploring a particular issue or subject. 

verb
  • To move forth, as into battle. 

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. 

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