adusk vs lightless

adusk

adj

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

adv

  • At dusk; in the dusk or twilight. 

lightless

adj

  • Lacking light; unilluminated; dark. 

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