preface vs usher

preface

verb
  • To give a preface to. 

  • To introduce or make a comment before (the main point). 

noun
  • An introduction, or series of preliminary remarks. 

  • A title or epithet. 

  • The beginning or introductory portion that comes before the main text of a document or book. 

  • The prelude or introduction to the canon of the Mass. 

usher

verb
  • To precede; to act as a forerunner or herald. 

  • To lead or guide somewhere. 

  • To accompany or escort (someone). 

  • To guide people to their seats. 

noun
  • A male escort at a wedding. 

  • A doorkeeper in a courtroom. 

  • A person, in a church, cinema etc., who escorts people to their seats. 

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