crepusculum vs midnight

crepusculum

noun
  • crepuscule; twilight; dusk 

midnight

noun
  • The middle of the night: the sixth temporal hour, equidistant between sunset and sunrise. 

  • Twelve o'clock at night exactly. 

  • Synonym of boxcars (“a pair of sixes”) 

adj
  • Utterly dark or black. 

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