blood brother vs relationship

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. 

relationship

noun
  • Kinship; being related by blood or marriage. 

  • The level or degree of affinity between keys, chords and tones. 

  • The links between the x-values and y-values of ordered pairs of numbers especially coordinates. 

  • Connection or association; the condition of being related. 

  • A romantic or sexual involvement. 

  • A way in which two or more people behave and are involved with each other 

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