Where does “riuten” come from?

riuten (Old High German) comes from Proto-West Germanic reudan, from Proto-Germanic reudaną, from Proto-Indo-European h₁rewdʰ- — red.

Ancestry of “riuten”, step by step

Step	Language	Word	Meaning
1	Proto-West Germanic	reudan	to redden, to make red; to clear, to eradicate
2	Proto-Germanic	reudaną	to redden, make red; to clear, eradicate, remove
3	Proto-Indo-European	h₁rewdʰ-	red

riuten — Etymology, Origin & Word History | Etymology Explorer