precursor vs usher

precursor

adj
  • Caused by the following symbol. 

noun
  • One of the compounds that participates in the chemical reaction that produces another compound. 

  • That which precurses: a forerunner, predecessor, or indicator of approaching events. 

usher

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. 

verb
  • To lead or guide somewhere. 

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

  • To accompany or escort (someone). 

  • To guide people to their seats. 

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