This article investigates the story of the origin and the expanse of the term caesar in the Indo-European languages. A hypothesis on the non-existence of the diphthongs /ai/ and /au/ in Gothic is used to show that the borrowing into Gothic occurred from Greek and renders the Greek spelling practice. Due to additional facts concerning the monophthongization of the diphthong /ai/ in Greek and Latin it is hypothesized that they might already represent not a diphthong but a single vowel. Counter-evidence is also stated, as the precise way of the borrowing still remains unknown.