Where does “Vritra” come from?

Vritra (English) comes from Sanskrit वृत्र, from Proto-Indo-Aryan wr̥trás, from Proto-Indo-Iranian wr̥trás — shield, cover, obstacle.

Ancestry of “Vritra”, step by step

Step	Language	Word	Meaning
1	Sanskrit	वृत्र	"coverer, investor, restrainer", an enemy, foe,...
2	Proto-Indo-Aryan	wr̥trás	—
3	Proto-Indo-Iranian	wr̥trás	shield, cover, obstacle

Vritra — Etymology, Origin & Word History | Etymology Explorer