blood brother vs stepfather

blood brother

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

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

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

stepfather

noun
  • A husband of one's parent distinct from one's biological father 

  • A husband of one's biological mother after her initial marriage to or relationship with one's biological father. 

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