Blood Brother

What does Blood Brother mean in American Law?

The definition of Blood Brother in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

A brother by commonality of parentage, rather than by adoption or intermarriage of the surviving members of each pair of parents. See stepchild. It is unclear if “blood brother” is used for children related by half blood, i.e., those sharing only one biological parent. See brother. (The usage for female siblings would seem to be “blood sister,” but it is hardly ever seen.) “Blood brother,” however, is most commonly used to emphasize a close relationship with a person not related to him by blood; when a person says another is his “blood brother” he ordinarily is asserting that he is like one (in loyalty, identification of interests, etc.) despite the lack of biological connection. Sometimes a ceremony turning on the double meaning of blood (physical substance and shared heredity) is involved: The “blood brothers” superficially wound themselves and mingle the blood that flows. But this seems confined today to “primitive” tribes and romantic young boys.