Zarathustra Syllabification: (Zar·a·thus·tra)Pronunciation: /ˌzarəˈTHo͞ostrə/Definition of Zarathustra the Avestan name for the Persian prophet Zoroaster. Derivatives ZarathustrianPronunciation: /-ˈTHo͞ostrēən/ adjective & noun Zarathustra in other Oxford dictionaries Definition of Zarathustra in the British & World English dictionary