Where does “tartre” come from?

tartre (Old French) comes from Medieval Latin tartarum, from Byzantine Greek τάρταρον, from Arabic دُرْدِيّ, from Persian درد, from Proto-Iranian *dr̥ti-, from Proto-Indo-European *dʰṛ-to-, from Proto-Indo-European dʰreyd- — to have diarrhea.

tartre (Old French): flat pastry