quality:correction, linguistic:translation
Etymology and nomenclature

Tacitus called it the Suebic Sea, Latin: Mare Suebicum after the Germanic people of the Suebi, and Ptolemy Sarmatian Ocean after the Sarmatians, but the first to name it the Baltic Sea (Medieval Latin: Mare Balticum) was the eleventh-century German chronicler Adam of Bremen. The origin of the latter name is speculative and it was adopted into Slavic and Finnic languages spoken around the sea, very likely due to the role of Medieval Latin in cartography. It might be connected to the Germanic word belt, a name used for two of the Danish straits, the Belts, while others claim it to be directly derived from the source of the Germanic word, Latin balteus "belt". Adam of Bremen himself compared the sea with a belt, stating that it is so named because it stretches through the land as a belt (Balticus, eo quod in modum baltei longo tractu per Scithicas regiones tendatur usque in Greciam).

He might also have been influenced by the name of a legendary island mentioned in the Natural History of Pliny the Elder. Pliny mentions an island named Baltia (or Balcia) with reference to accounts of Pytheas and Xenophon. It is possible that Pliny refers to an island named Basilia ("the royal") in On the Ocean by Pytheas. Baltia also might be derived from "belt", and therein mean "near belt of sea, strait".

Others have suggested that the name of the island originates from the Proto-Indo-European root *bʰel meaning "white, fair", which may echo the naming of seas after colours relating to the cardinal points (as per Black Sea and Red Sea). This '*bʰel' root and basic meaning were retained in Lithuanian (as baltas), Latvian (as balts) and Slavic (as bely). On this basis, a related hypothesis holds that the name originated from this Indo-European root via a Baltic language such as Lithuanian. Another explanation is that, while derived from the aforementioned root, the name of the sea is related to names for various forms of water and related substances in several European languages, that might have been originally associated with colors found in swamps (compare Proto-Slavic *bolto "swamp"). Yet another explanation is that the name originally meant "enclosed sea, bay" as opposed to open sea.

In the Middle Ages the sea was known by a variety of names. The name Baltic Sea became dominant after 1600. Usage of Baltic and similar terms to denote the region east of the sea started only in the 19th century.