agnate vs blood brother

agnate

noun
  • A relative whose relation is traced only through male members of the family. 

  • A statement having a similar meaning to another, but a different structure. 

  • Any paternal male relative. 

adj
  • allied; akin 

  • Related to someone by male connections or on the paternal side of the family. 

  • Having a similar semantic meaning. 

blood brother

noun
  • 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. 

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

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