preliminary vs prolegomenon

preliminary

noun
  • A preparation for a main matter; an introduction. 

  • Any of a series of sports events that determine the finalists 

  • A relatively minor contest that precedes a major one, especially in boxing 

adj
  • In preparation for the main matter; initial, introductory, preparatory. 

prolegomenon

noun
  • A prefatory discussion; a formal essay or critical discussion serving to introduce and interpret an extended work. 

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