first night vs initiatory

first night

noun
  • Used other than figuratively or idiomatically: see first, night. 

  • The first night after marriage. 

  • The first public performance of a play or other show, normally assumed to be held in the evening. 

initiatory

noun
  • An introductory act or rite. 

adj
  • Of or pertaining to initiation 

  • inceptive, initial, inaugural or introductory 

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