Ultimately from Proto-Iranian *ra(n)ǰ- (“to colour, dye”) (compare Sogdian [script needed] (rɣš- /raxš/, “Rakhsh”), Chorasmian rxtk (raxtak, “red”), Mazanderani رش (raš, “red (of cattle)”), Kurdish reş (“black”)), from Proto-Indo-Iranian (compare Sanskrit रञ्ज् (rañj, “to be dyed or coloured, to redden, grow red, glow”)), from Proto-Indo-European *reg- (“to dye”).
The Persian word is not inherited but is borrowed probably from the Sogdian cognate.
رخش • (raxš)
رخش • (Raxš)
- Rakhsh, the horse of Rustam
رخش • (roxš)