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1590s, from Russian kozak, from Turkish kazak "adventurer, guerilla, nomad," from qaz "to wander." The same Turkic root is the source of the people-name Kazakh and the nation of Kazakhstan.
A people in southern Russia who became aggressive warriors during the sixteenth and seventeenth centuries. In place of taxes, they supplied the Russian Empire with scouts and mounted soldiers. The Cossacks are also famed for their dances, which feature fast-paced music and seemingly impossible leaps.