adusk vs stygian

adusk

adj

  • Resembling conditions at dusk or twilight, low-lit, dark; in darkness, gloomy. 

adv

  • At dusk; in the dusk or twilight. 

stygian

adj

  • Dark and gloomy. 

  • Having a luminosity below 0%. 

  • Infernal or hellish. 

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