Which sea's name comes from the Greek for 'inhospitable', later renamed 'hospitable'?

The Black Sea, called Axeinos - inhospitable - by early Greek sailors, and then renamed Euxeinos, hospitable, once colonies had been established around it. The rename is usually read as either optimism or superstition: you do not want to be sailing on something called unfriendly.

It is the largest body of anoxic water on Earth. Below about 150 metres there is no oxygen at all and no exchange with the surface layer, because fresh water from the Danube and the Dnieper floats on denser salt water coming in from the Mediterranean - so ninety per cent of its volume is dead, inhabited only by bacteria that produce hydrogen sulphide.

That has made it an accidental museum. Wood-boring molluscs cannot live without oxygen, so ships that sank there do not decay - a Greek merchant vessel found in 2018 at 2,000 metres, dated to about 400 BC, is the oldest intact shipwreck known, complete with mast and rowing benches. There is also a contested hypothesis that the basin flooded catastrophically from the Mediterranean around 5600 BC and that the event lies behind Near Eastern flood narratives, which the geological evidence has not settled.