What is a sacrifice, or ceremony, by which cities, fields, armies, or people, defiled by crimes, pestilence, or other cause of uncleanness, were purified called?

lustration — (Antiq.) A sacrifice, or ceremony, by which cities, fields, armies, or people, defiled by crimes, pestilence, or other cause of uncleanness, were purified. (Webster's 1913.)

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