θάλαττα (θάλασσα)

In common language, the sea is a huge open water where the opposite coast cannot be seen.

The modern scientific definition differs from the mere experience and considers the arrangement of land around the water and the amount of salt in it. This causes several misnamed areas like the Baltic Sea, the Caspean Sea, the Black Sea, ... which are inland lakes due to the modern definition.

For Aristotle and other ancient authors, the "common language"-definition applies.