1. Mythology. A legendary island, first mentioned by Plato, said to have existed in the Atlantic Ocean west of Gibraltar and to have sunk beneath the sea, but linked by some modern archaeologists with the island of Thera, the surviving remnant of a much larger island destroyed by a volcanic eruption c1500 b.c.
EX. Finding a kid who's favorite super hero is Aquaman is like finding Atlantis-- and, coincidentally, Aquaman is the King of Atlantis in the DC Universe.