Definition: Aquatone is a term used in Greek mythology, referring to the liquid that flowed down the river Styx from the underworld into the sea. The word "aquatone" signifies the substance that flowed out of the underworld (meaning the underworld was inhabited by demons and was considered the place where hell came to dwell), causing chaos in the mortal world. This substance was liquid, similar to a stream of water or any other fluid, hence the name "aquatone."