crepusculum vs nocturnal

crepusculum

noun
  • crepuscule; twilight; dusk 

nocturnal

noun
  • A device for telling the time at night, rather like a sundial but read according to the stars. 

  • A person or creature that is active at night. 

adj
  • Taking place at night, nightly. 

  • Primarily active during the night. 

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