(especially in czarist Russia) a person belonging to any of certain groups of Slavs living chiefly in the southern part of Russia in Europe and forming an elite corps of horsemen.
Origin: 1590–1600; < Polish kozak or Ukrainian kozák, ultimately < a Turkic word taken to mean “adventurer, freebooter,” adopted as an ethnic name by Turkic tribal groups of the Eurasian steppes
(formerly) any of the free warrior-peasants of chiefly East Slavonic descent who lived in communes, esp in Ukraine, and served as cavalry under the tsars
—adj
2.
of, relating to, or characteristic of the Cossacks: a Cossack dance
[C16: from Russian kazak vagabond, of Turkic origin]
1598, from Rus. kozak, from Turk. quzzak "adventurer, guerilla, nomad," from qaz "to wander." The same Turkic root is the source of the people-name Kazakh and the nation of Kazakhstan.