The term originates from the name of the prophet Zoroaster, the Greek rendition of the Old Iranian name Zarathustra. The exact meaning of the prophet's name is debated but is thought to possibly combine elements meaning "old" or "moving" and "camel." The English adjective was formed in the 18th century by appending the common suffix '-ian', denoting "belonging to" or "relating to," directly to the prophet's Hellenized name. Thus, 'Zoroastrian' literally means "pertaining to Zoroaster," directly identifying the religion and its adherents with its foundational prophet.

The word is a proper name derivative and functions as a single, unsegmentable unit in modern English. It is derived from the name Zoroaster (the Greek form of the prophet's name, Zarathustra) + the English adjectival suffix '-ian'.