Someone bound to another person in commitment and friendship by a ceremonial mingling of blood
brother: a male with the same parents as someone else; "my brother still lives with our parents"
close friend, man who is in a close relationship; brother from birth, biological brother
a male sworn (usually by a ceremony involving the mingling of blood) to treat another as his brother
A man's blood brother is a man he has sworn to treat as a brother, often in a ceremony which involves mixing a small amount of their blood. a man who promises loyalty to another, often in a ceremony in which the men's blood is mixed together