Learn how to say Cossack correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word Cossack:
(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
of, relating to, or characteristic of the Cossacks ⇒ a Cossack dance
C16: from Russian kazak vagabond, of Turkic origin