the.com/blood brother

means A man bonded to another—often through a ritual exchange of blood—as a brother by choice rather than birth, with loyalty meant to outlast any contract.

from The phrase is a plain compound of 'blood' (kinship, lineage, the stuff that supposedly carries loyalty) and 'brother,' describing a bond made rather than born. The underlying practice—mixing blood to seal a pact—shows up across many cultures and centuries, often called a 'blood oath' or 'blood covenant,' on the logic that sharing blood ritually mimics sharing it by birth. The English term itself is old and straightforward, not traced to one single origin story, but to this widespread habit of humans deciding that handshakes aren't binding enough.