Zam
m (Zām) is the Avestan language term for the Zoroastrian concept of "earth", in both the sense of land and soil and in the sense of the world. The earth is prototyped as a primordial element in Zoroastrian tradition, and represented by a minor divinity Zam who is the hypostasis of the "earth". The word itself is cognate to the Baltic 'Zemes' and Slavic 'Zem', both meaning the planet earth as well as soil.
The element zam exists with the same meaning in Middle Persian, which is the language of the texts of Zoroastrian tradition. The divinity Zam however appears in the later language as Zamyad, which is a contraction of "Zam Yazad", i.e. the yazata Zam.
Zam of the earth is not related to the Zam of the Shahnameh. That Zam—Zahhak-e-Maar-Doosh (Aži Dahāka in Avestan, Azhdshak in Middle Persian)—is the king of dragons that slew Jamshid.
Read more about Zam: In Scripture, In Tradition, References and Bibliography