The term 'disappear into the ETHER' is a metaphor for something that has vanished without a trace. It is often used to describe a situation in which something has been lost or forgotten, and it implies that the thing in question has been completely erased from existence. The crossword solution for this term is 'ETHER, ' which is a reference to the ancient Greek concept of the same name. In Greek mythology, the ETHER was believed to be a divine substance that filled the upper regions of the universe and was the source of all life. Thus, the phrase 'disappear into the ETHER' is a way of saying that something has been completely erased from existence.