1911 Encyclopedia Britannica
Avenger of Blood
The person, usually the nearest kinsman of the murdered man, whose duty it was to avenge his death by killing the murderer. In primitive societies, before the evolution of settled government, or the uprise of a systematized criminal law, crimes of violence were regarded as injuries of a personal character to be punished by the sufferer or his kinsfolk. This right of vengeance was common to most countries, and in many was the subject of strict regulations and limitations. It was prevented from running into excesses by the law of sanctuary and in many lands the institution of blood-money, and the wergild offered the wrong-doer a mode of escaping from his enemies' revenge. The Mosaic law recognized the right of vengeance, but not the money-compensation. The Koran, on the contrary, while sanctioning the vengeance, also permits pecuniary commutation for murder.
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Chisholm, Hugh, General Editor. Entry for 'Avenger of Blood'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/a/avenger-of-blood.html. 1910.