Cossack
Concise Oxford English Dictionary © 2008 Oxford University Press:
Cossack /ˈkɒsak/
▶noun a member of a people of southern Russia, Ukraine, and Siberia, noted for their horsemanship and military skill.
– origin from Russ. kazak from Turkic, ‘vagabond, nomad’; later influenced by Fr. Cosaque (cf. Kazakh).
'Cossack' also found in these Oxford entries:

