adusk vs tenebrous

adusk

adj

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

adv

  • At dusk; in the dusk or twilight. 

tenebrous

adj

  • dark and gloomy 

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