Where does “Zoroastrianism” come from?

Zoroastrianism is an English formation from Zoroastrian, derived through Latin -ianus and -ius suffixes from Proto-Indo-European -yós via Proto-Italic -os.

Ancestry of “Zoroastrianism”, step by step

Step	Language	Word	Meaning
1	English	Zoroastrian	a follower of Zoroastrianism; relating to or...
2	Latin	Zōroastrēs	—
3	Ancient Greek	Ζωροάστρης	—
4	Avestan	𐬰𐬀𐬭𐬀𐬚𐬎𐬱𐬙𐬭𐬀	—

Every word from Avestan 𐬰𐬀𐬭𐬀𐬚𐬎𐬱𐬙𐬭𐬀 →

Zoroastrianism — Etymology, Origin & Word History | Etymology Explorer