Where does “Γαληνός” come from?

Γαληνός (Ancient Greek) comes from Ancient Greek γαλήνη, from Proto-Indo-European ǵelh₂-.

Ancestry of “Γαληνός”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	γαλήνη	calm, stillness of wind or sea; galena, lead...
2	Proto-Indo-European	ǵelh₂-	—

Γαληνός — Etymology, Origin & Word History | Etymology Explorer