initialism vs precursory

initialism

noun
  • The process of forming words or terms using initial letters of other words. 

  • A term formed from the initial letters of several words or parts of words, which is itself pronounced letter by letter. 

precursory

noun
  • A precursor; a sign of the onset of something. 

adj
  • Being or relating to a precursor; relating to events that will follow. 

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