Its source is an English expression meaning "The ocean."
This is the name of the ocean that lies between the western shores of the Old World and the eastern shores of the New. It is sometimes given to a child born at sea.
It probably derives from the name of the Atlas mountains in North Africa. That name originated with a Greek myth in which Zeus gives a rebellious Titan named Atlas the task of holding up the heavens. The mountains are his transformed body, straining under its titanic load.