"pertaining to or connected with the former electorate of Hanover in northern Germany, from the German city of Hanover (German Hannover), literally "on the high ridge," from Middle Low German hoch "high" + over, cognate with Old English ofer "flat-topped ridge." The modern royal family of Great Britain is descended from Electoress Sophia of Hannover, grand-daughter of James I of England, whose heirs received the British crown in 1701 (nearer heirs being set aside as Roman Catholics). The first was George I. They were joint rulers of Britain and Hannover until the accession of Victoria (1837) who was excluded from Hannover by Salic Law. Hanover in English also was a euphemism for "Hell."
[Hanoverian etymology, Hanoverian origin, 英语词源]