Russian

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mid 16th century: from medieval Latin Russianus .

wiktionary

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Medieval Latin (11th century) Russiānus, the adjective of Russia, a Latinization of the Old East Slavic Русь(Rusĭ). Attested in English (both as a noun and as an adjective) from the 16th century.

etymonline

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Russian (n.)

1530s, from Medieval Latin Russianus, from Russia (see Russia). Slang or colloquial Russki "Russian" (1858) is from Russian Russkiy. Russian roulette attested from 1937. Russian dressing for salads is from 1915.