Also known in more dated English as Sleswick-Holsatia, the Danish name is Slesvig-Holsten, the Low German name is Sleswig-Holsteen, and the North Frisian name is Slaswik-Holstiinj. Historically, the name can also refer to a larger region, containing both present-day Schleswig-Holstein and the former South Jutland County (Northern Schleswig) in Denmark.
The term "Holstein" derives from Old Saxon Holseta Land, (Holz and Holt mean wood in modern Standardised German and in literary English, respectively). Originally, it referred to the central of the three Saxon tribes north of the River Elbe: Tedmarsgoi (Dithmarschen), Holstein and Sturmarii (Stormarn). The area of the tribe of the Holsts was between the Stör River and Hamburg, and after Christianization, their main church was in Schenefeld. Saxon Holstein became a part of the Holy Roman Empire after Charlemagne's Saxon campaigns in the late eighth century. Since 811, the northern frontier of Holstein (and thus the Empire) was marked by the River Eider.
The term Schleswig comes from the city of Schleswig. The name derives from the Schlei inlet in the east and vik meaning inlet in Old Norse or settlement in Old Saxon, and linguistically identical (cognate) with the "-wick" or "-wich" element in place-names in Britain.
The Duchy of Schleswig or Southern Jutland was originally an integral part of Denmark, but was in medieval times established as a fief under the Kingdom of Denmark, with the same relation to the Danish Crown as for example Brandenburg or Bavaria vis-à-vis the Holy Roman Emperor. Around 1100, the Duke of Saxony gave Holstein, as it was his own country, to Count Adolf I of Schauenburg.
Schleswig and Holstein have at different times belonged in part or completely to either Denmark or Germany, or have been virtually independent of both nations. The exception is that Schleswig had never been part of Germany until the Second Schleswig War in 1864. For many centuries, the King of Denmark was both a Danish Duke of Schleswig and a German Duke of Holstein. Essentially, Schleswig was either integrated into Denmark or was a Danish fief, and Holstein was a German fief and once a sovereign state long ago. Both were for several centuries ruled by the kings of Denmark. In 1721, all of Schleswig was united as a single duchy under the king of Denmark, and the great powers of Europe confirmed in an international treaty that all future kings of Denmark should automatically become dukes of Schleswig, and consequently Schleswig would always follow the same order of succession as the one chosen in the Kingdom of Denmark. In the church, following the reformation, German was used in the southern part of Schleswig and Danish in the northern part. This would later prove decisive for shaping national sentiments in the population, as well as after 1814 when mandatory school education was introduced. The administration of both duchies was conducted in German, despite the fact that they were governed from Copenhagen (from 1523 by the German Chancellary which was in 1806 renamed Schleswig-Holstein Chancellary).