Where does “అరుణుడు” come from?

అరుణుడు (Telugu) comes from Sanskrit अरुण, from Proto-Indo-Iranian *Harunás.

Ancestry of “అరుణుడు”, step by step

Step	Language	Word	Meaning
1	Sanskrit	अरुण	a name for the sun; also of his charioteer, or...
2	Proto-Indo-Iranian	*Harunás	—

అరుణుడు — Etymology, Origin & Word History | Etymology Explorer