
The oprichnina (опри́чнина, IPA) is the period of Russian history between 1565 and 1572 during which Tsar Ivan the Terrible instituted a domestic policy of secret police, mass repressions, public executions, and confiscation of land from Russian aristocrats. The six thousand political police enforcing the policy were called oprichniki, a...
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http://en.wikipedia.org/wiki/Oprichnina

private court or household created by Tsar Ivan IV the Terrible (1565) that administered those Russian lands (also known as oprichnina) that had ... [2 related articles]
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http://www.britannica.com/eb/a-z/o/24

originally, the personal possessions of a prince or the dower of his widow; under Ivan the Terrible, those persons (oprichniki) and sections of the country under the tsar's personal command, and outside the normal administrative structure of the state.
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http://www.uleth.ca/lib/digitized_collections/ourheritage/Great_Adventures/

The era in the 1550s during which Ivan IV (the Terrible) brutally punished and decimated the boyar (q.v.) class.
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https://irp.fas.org/world/russia/su_glos.html
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