An Etymological Dictionary of the German Language/Annotated/Kaiser
Kaiser, masculine, ‘emperor,’ from the equivalent Middle High German keiser, Old High German keisar; corresponding to Anglo-Saxon câsêre, Gothic kaisar. The ai of the Modern High German orthography originated in the Bavarian and Austrian chancery of Maximilian I., in which the Middle High German ei necessarily became ai (according to the lexicographer Helvig, A.D. 1620, Meissen Saxon Keiser was Bohemian-Bavarian Kayser). The ae of Latin Caesar, upon which the word is based, cannot be made responsible for the Modern High German ai. Moreover, the relation of Latin ai to Gothic-Teutonic ai is not explained. The Romans, it is true, used ae for ai in Teutonic words, compare Latin gaesum, under Ger; yet the use of Teutonic ê to represent ae in Latin Graecus (Gothic Krêks, Old High German Chriah, ‘Greek’) is opposed to this. At the same period as the adoption of the names Grieche and Römer (Gothic Rûmôneis), i.e., the beginning of our era, the Teutons must have borrowed the Latin term, connecting it chiefly with Caius Julius Cæsar (similarly the Slavs use the name Karl der Große of Charlemagne, in the sense of ‘king’; Old Slavonic kraljǐ, Russian korolǐ, whence Lithuanian karálius, ‘king’); yet not until the Roman emperors adopted the title Cæsar could this word, which probably existed previously in Teutonic, assume the meaning ‘emperor,’ while the Romance nations adhered to the Latin title imperator; compare French empereur. Old Slovenian césarǐ (in Russian contracted Car) is derived through a German medium (which also elucidates Middle English and Old Icelandic keiser) from Cæsar. Thus Kaiser is the earliest Latin word borrowed by Teutonic (see Hanf). For a Kelt loan-word meaning ‘king’ see under Reich.