Where does “دین” come from?

دین (Classical Persian) comes from Arabic دين, from Middle Persian dyn', from Avestan 𐬛𐬀𐬉𐬥𐬁, from Proto-Iranian *dáyHanaH.

Ancestry of “دین”, step by step

Step	Language	Word	Meaning
1	Arabic	دين	verbal noun of دَانَ; religion, creed, credo,...
2	Middle Persian	dyn'	—
3	Avestan	𐬛𐬀𐬉𐬥𐬁	religion
4	Proto-Iranian	*dáyHanaH	—

دین — Etymology, Origin & Word History | Etymology Explorer