blood libel

noun

: the false and maliciously perpetuated accusation that Jews have murdered non-Jews (such as Christian children) in order to use their blood in rituals

… an extensive description of Christian mistreatment of Jews in the Middle Ages, beginning with the Crusades, then tracing the rise of tales of blood libel, and ending with the forced conversion of Jews during the Inquisition …—

Robert Louis Wilken, Commonwealth, 26 Jan. 2001

… the pervasiveness of blood in the most incendiary and murderous of anti-Semitic legends: the so-called blood libel—the persistent legend that Jews practice the ritual murder of Christian children (a kind of recapitulation of the Crucifixion) in order to obtain blood for use in Passover rituals.—

Ron Rosenbaum, Explaining Hitler, 1988

: an instance of such an accusation being made

The infamous series of medieval blood libels against Jews began in Norwich, England, in 1144, and continued, with slight variations, down to the twentieth century, often serving as an excuse for massacring the Jews.—

Raphael Patai et al., The Myth of the Jewish Race, 1989

… the coat of arms of the city of Trent (the site of a notorious blood libel in 1475) …—

Elliott Horowitz, New Republic, 25 Sept. 2000