blood brother

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Poverty and pride are devoted blood brother until one, always and inevitably, kill the other.
贫穷与自尊是歃血为盟的拜把兄弟，但最终总是有一方会杀死另一方。
zhoukan.cc
Whoever they are, they will never know that they are a blood brother or sister to an Australian!
不管他们是谁，他们绝不会知道自己是一个澳大利亚人的血亲兄弟或姐妹。
edu.sina.com.cn
He's not necessarily talking about your physical brother, your blood brother, but he's also not talking about just any human being.
他说的并不是你亲生的弟兄，你的亲哥哥亲弟弟，也不是说所有人类。

And right now we have Hugo Chavez who's a blood brother of Fidel Castro, and he has used millions and millions of dollars to influence the elections in Bolivia and Nicaragua and elsewhere.
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On his side, Rothschild has mustered Hashim Djojohadikusumo, a blue-blood Indonesian businessman and brother of presidential aspirant Prabowo Subianto.
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The caricature of Amy as the demonic sister who sought inspiration in the pages of the National Enquirer before murdering her brother in cold blood is too facile, as is the cynical narrative of a secret handshake between John Polio and Judy Bishop that kept the truth buried for decades.
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a man who has promised to treat another man as his brother in a ceremony in which they cut themselves and mix their blood together

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.