From Middle EnglishGersey, from Anglo-NormanGersui, further etymology disputed. Probably from Old Norse[Term?], compound of Geirs(“Geirr's”) +ey(“island”). Also occasionally and historically connected to LatinCaesarea, a common name given to locations conquered by the Romans in honor of Caesar (compare French Césarée). The latter theory still bestows the Latin translation of the island.
2018, Oliver Bullough, chapter 3, in Moneyland, Profile Books, →ISBN:
The resilience of Jersey’s elite is not new (Jersey is perhaps the only place in Europe that had the same government before, during and after Nazi occupation) but it had never previously been described with such forensic force.