Anglicized form of Gaelic Domhnall. The final -d of the Anglicized form derives partly from misinterpretation by English speakers of the Gaelic pronunciation, and partly from association with Germanic-origin names such as Ronald. This name is strongly associated with clan Macdonald, the clan of the medieval Lords of the Isles, but is now also widely used by families with no Scottish connections.
Czech: occupational name for a merchant or dealer, Czech soukup (from Slavic sou- ‘with’ + kup ‘buy’). The vocabulary word later acquired the sense ‘fence’, i.e. ‘one who receives stolen property or abets a thief’, but this is probably irrelevant to the surname, which was formed before this sense was established.