In Imperial Russia: a secret police department set up in 1881 (after the assassination of Tsar Alexander II) to maintain state security and suppress revolutionary activities, and abolished after the February Revolution in 1917 (now historical). Also (in later and extended use): the security services of the Soviet Union or its successors.
Late 19th century; earliest use found in The Times. From Russian oxrana, lit. ‘guarding, protection, security’, colloquial use of noun (from oxran- (stem of oxranjat′, oxranit′ to guard, protect) + -a, suffix forming feminine nouns) to represent the fuller and more official name for the organization, oxrannoe otdelenie security department.