darkling vs nigrescent

darkling

adj
  • Dark; growing dark; darkening. 

  • Obscure; taking place unseen, as if in the dark. 

noun
  • A creature that lives in the dark. 

  • Darkness 

adv
  • In the dark; in obscurity. 

nigrescent

adj
  • Approaching blackness; blackish, dark-coloured. 

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