at night vs diurnal

at night

adv
  • During the night. 

diurnal

adj
  • Happening or occurring during daylight, or primarily active during that time. 

  • Said of a flower open, or releasing its perfume during daylight hours, but not at night. 

  • Done once every day; daily, quotidian. 

  • Having a daily cycle that is completed every 24 hours, usually referring to tasks, processes, tides, or sunrise to sunset; circadian. 

noun
  • A flower that opens only in the day. 

  • A book containing canonical offices performed during the day, hence not matins. 

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