blood libel

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The false accusation that Jews murder non-Jewish children to use their blood for their religious rituals and holidays.
• noun by extension Any false or purportedly false accusation of murder of a non-Jew by a Jewish person or organization.
• noun by extension Any false or purportedly false accusation of guilt, especially of guilt in mass murder or homicide.
• noun More generally, any canard or virulent lie about someone.