1.nounA member or descendant of an originally (semi-)nomadic population of Eastern Europe and the adjacent parts of Asia, formed in part of runaways from the neighbouring countries, that eventually settled in parts of the Polish-Lithuanian Commonwealth and the Russian tsarist Empire (where they constituted a legendary military caste), particularly in areas now comprising southern Russia and Ukraine.
2.nounA member of a military unit (typically cavalry, originally recruited exclusively from the above)