Word Origin & History
"an emperor," O.E. casere, obscure after M.E., but revived 1858 in ref. to the Ger. emperors of Austria and, after 1870, Germany, from Ger. Kaiser, from Bavarian and Austrian spelling of M.H.G. keisar, from O.H.G. keisar "emperor," an early borrowing of L. cognomen Cæsar (q.v.). The Gmc. and Slavic
peoples seem to have called all Roman emperors "caesar" (cf. O.E. casere, O.N. keisari). Said to be the earliest L. loan word in Gmc.