Acherusia ('Αχερουσια λιμνη or 'Αχερουσις), a name given by the ancients to several lakes or
swamps, which, like the various rivers of the name of
Acheron, were at some time believed to be connected with
the lower world, until at last the Acherusia came to be considered to be in the lower world itself.
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[Greek heroic] A cavern on the borders of Pontus, through which Heracles dragged Cerberus from the infernal regions to earth.