black man vs nigga

black man

noun
  • A male adult member of an ethnic group having dark pigmentation of the skin, typically of sub-Saharan African descent; or the appearance thereof. 

  • Used other than figuratively or idiomatically: see black, man. 

nigga

noun
  • A black person (usually male), especially an African American. 

  • A male as opposed to a female. 

  • A close and loyal friend. 

  • Any person, though chiefly male. 

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