The right spelling of the name in Avestan is "Zarathushtra". It is the ancient form as it is given in the Gathas. Also other forms exist because the teaching of Zarathustra was spread in the different regions. So, we have Zoroaster in Greek, Zartosht in Persian, Zardusht in Gujarati etc. "Zarathustra" is the combined form of "Zarathushtra" and Greek "Zoroaster".

According to linguistics, the word Zarathustra means “golden shinning star” : "Zar-" means "gold". "-ushtra" comes from "ush-" (shining)+ " stra" (the star).

Some scholars say, however that "-tu-" in "-tushtra" means "two",and it makes the name "The golden shining double star", or "The Golden Sirius", as "-tushtra" and "tishtrya"/"tishtar" can be the same words,and the Sirius is indeed the double star.