The story
The origin is unknown. Attested as Arabic خَزَر (ḵazar), Medieval Greek Χάζαροι (Kházaroi), Hebrew כּוּזָרִים (Kuzarim), Middle Chinese 突厥曷薩 (*tʰuət̚-kɨut̚ ɦɑt̚-sɑt̚) and Middle Chinese 突厥可薩部 (*tʰuət̚-kɨut̚ kʰɑ^X-sɑt̚ buo^X), Latin Gazari and Cosar, Old Armenian խազիրք (xazirkʻ), Old East Slavic козаринъ (kozarinŭ), Persian خزر (xazar), Russian хаза́р (xazár), Tatar хәзәр (xäzär), Turkish Hazar, etc. Compare Old Uyghur 𐰴𐱁𐰺 (qšr¹), Middle Persian [script needed] (Kesar), Tibetan [script needed] (ge-sar). See Wikipedia's article for etymology.
Etymology from Wiktionary, CC BY-SA 4.0.