FiveRiversOfHades

There were five main rivers that appear both in the real world and the underworld. Their names were meant to reflect the emotions associated with death.[5]

• The Styx is generally considered to be one of the most prominent and central rivers of the Underworld and is also the most widely known out of all the rivers. It is known as the river of hatred and is named after the goddess Styx. This river circles the underworld seven times.[6]
• The Acheron is the river of pain. It is the river that Charon, also known as the Ferryman, rows the dead over according to many mythological accounts, though sometimes it is the river Styx or both.[7]
• The Lethe is the river of forgetfulness. It is associated with the goddess Lethe, the goddess of forgetfulness and oblivion. In later accounts a poplar branch dripping with water of the Lethe became the symbol of Hypnos, the god of sleep.[8]
• The Phlegethon is the river of fire. According to Plato, this river led to the depths of Tartarus.
• The Cocytus is the river of wailing.
  

Eunoe (Greek: Εὐνοε) is a feature of Dante’s Commedia created by Dante as the fifth river of the dead (taking into consideration that Cocytus was described as a lake rather than a river). Penitents reaching the Garden of Eden at the top of Mount Purgatory are first washed in the waters of the river Lethe in order to forget the memories of their mortal sins. They then pass through Eunoe to have the memories of their good deeds in life strengthened.
Upon completing his or her sentence in Purgatory, a soul is washed in the rivers Lethe and Eunoe (in that order) by Matilda. It is unclear who Matilda was in real life, but, nonetheless, her function is to cause the penitent to forget his or her sins (now that these sins have been purgated) and then sip from the waters of Eunoe so that the soul may enter heaven full of the strength of his or her life’s good deeds.
Dante makes particular reference to the dolce ber or “sweet drink/draught” of Eunoe at the end of Purgatorio when he explains that he wished he had greater space to write of the water that “never would have sated me.” (trans. C.S. Singleton)

The word “eunoe” is one of Dante’s many neologisms presumably derived from Greek “eu-,” meaning “good” and “noe,” meaning “mind.”