Where does “ποτᾰμός” come from?

ποτᾰμός (Ancient Greek) comes from Proto-Indo-European peth₂- — to spread out; to fly.

Ancestry of “ποτᾰμός”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	peth₂-	to spread out; to fly

ποτᾰμός — Etymology, Origin & Word History | Etymology Explorer