corvid vs nigrescent

corvid

adj
  • Pertaining to or resembling the Corvidae. 

noun
  • A member of the bird family Corvidae, including crows, ravens, jays, choughs, treepies etc. 

nigrescent

adj
  • Approaching blackness; blackish, dark-coloured. 

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