nail: [OE] The Indo-European ancestor of nail was *nogh- or *onogh-. The latter was the source of Latin unguis (which evolved into French ongle and Italian unghia and has given English ungulate [19]) and Greek ónux (source of English onyx). Both these strands refer only to the sort of nails that grow on fingers and toes, but the Germanic branch of the family (which has come from *nogh- through a prehistoric Germanic *naglaz) has differentiated into a ‘fastening pin’ – originally of wood, latterly of metal.
Hence English nail and German nagel cover both meanings (although Dutch and Swedish nagel and Danish negl are used only for the anatomical ‘nail’). => onyx, ungulate[nail etymology, nail origin, 英语词源]