big brother vs blood brother

big brother

noun
  • A sibling's older brother. 

  • Something that is bigger in comparison. 

blood brother

noun
  • A brother by blood: a brother-german or half-brother, as distinguished from step-brothers. 

  • An unrelated male considered to share such a strong relationship generally. 

  • An unrelated male considered to share a brother-like relationship established by a ceremonial sharing of blood in some cultures. 

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