initiatory vs preliminary

initiatory

adj
  • inceptive, initial, inaugural or introductory 

  • Of or pertaining to initiation 

noun
  • An introductory act or rite. 

preliminary

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

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

  • A preparation for a main matter; an introduction. 

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

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