Where does “रक्ताक्ष” come from?

रक्ताक्ष (Sanskrit) comes from Sanskrit अक्ष, from Proto-Indo-Iranian Háćšas, from Proto-Indo-European h₂éḱs-os.

रक्ताक्ष (Sanskrit): red-eyed, having red or blood-shot eyes R. BhP;...

Definitions

रक्ताक्ष traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Sanskrit	अक्ष	axle, axis; wheel, car, cart; the beam of a...
2	Proto-Indo-Iranian	Háćšas	axle
3	Proto-Indo-European	h₂éḱs-os	—

Step	Language	Word	Meaning
1	Sanskrit	रक्त	red; safflower L; Barringtonia acutangula L
2	Sanskrit	रञ्ज्	to redden; to dye or color
3	Proto-Indo-European	*(s)reg-	—