constantly vs nocturnal

constantly

adv
  • In an unchangeable or invariable manner; in every case. 

  • In a constant manner; occurring continuously; persistently. 

  • Recurring regularly. 

nocturnal

adj
  • Taking place at night, nightly. 

  • Primarily active during the night. 

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. 

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