Kaiser

Inherited from Middle English kayser, from Old High German keisar (“emperor”), from Proto-West Germanic *kaisar, from Proto-Germanic *kaisaraz, from Latin Caesar. The native Old English descendant of that Proto-Germanic word was cāser (“emperor”), but the shape of Middle English kayser (“emperor”) (versus the expected *caser, *coser) suggests it was borrowed from another Germanic language rather than inherited, and the modern English spelling and sense seem to be modified after modern German rather than a direct continuation of Middle English. Compare tsar, which was borrowed from Slavic.

Doublet of Caesar and tsar.