PIE *swedh「自己」から。語源的にはself「慣用句」「習慣」と同じ*sweの拡大形。
Although the term 'ethnic cleansing' has come into English usage only recently, its verbal correlates in Czech, French, German, and Polish go back much further. [Jerry Z. Muller, "Us and Them: The Enduring Power of Ethnic Nationalism," Foreign Affairs, March/April 2008]