Sea

A caution before the names: Maria does not mean star of the sea. That reading goes back to a medieval interpretation of the name, probably originating in a copying error in Jerome, and it has been repeated ever since — including by a great many name sites. The actual origin of Miriam is uncertain and probably Egyptian. We mention it because it is the single most repeated false etymology in the whole subject, and because Marina, which genuinely does come from Latin marīnus, sits right beside it and is constantly confused with it.

With that set aside: Latin mare, Slavic morje and the Germanic word behind English mere are all inherited from one Indo-European root. It appears to have meant a body of standing water rather than an ocean specifically, which fits — the Proto-Indo-European homeland, wherever exactly it was, was not coastal.

The traditions that were coastal built their own vocabulary. Sanskrit has samudra and sāgara, Arabic baḥr, and the Polynesian and island languages a rich set of terms distinguishing reef, lagoon and open water in ways that European languages simply do not. Hawaiian kai and its relatives across the Pacific belong to a family with the longest continuous seafaring history of any on earth, and their naming shows it.

Greek supplies thalassa, a word with no secure Indo-European etymology and generally taken to be pre-Greek — a survival from whoever was in the Aegean before Greek speakers arrived.