preliminary vs prelusion

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. 

prelusion

noun
  • A prelude; something that comes first. 

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