Where does “ostai” come from?

ostai (Latvian) comes from Latvian osta, from Proto-Indo-European h₁óh₃s, from Proto-Indo-European h₁óh₃-s ~ h₁éh₃-s.

ostai (Latvian): dative singular form of osta

Definitions

Step	Language	Word	Meaning
1	Latvian	osta	port, harbor
2	Proto-Indo-European	h₁óh₃s	mouth
3	Proto-Indo-European	h₁óh₃-s ~ h₁éh₃-s	—

ostai — Etymology, Origin & Word History | Etymology Explorer