Phlegethon

UK: /ˈflɛɡɪˌθɒn/ US: (fleg′ə thon′, flej′-)

WordReference Random House Unabridged Dictionary of American English © 2025

Phleg•e•thon  (fleg′ə thon′, flej′-), n. 

1. Mythology Also called Pyriphlegethon. [Class. Myth.] a river of fire, one of five rivers surrounding Hades.
2. (often l.c.) a stream of fire or fiery light.

• Greek, noun, nominal use of phlegéthōn blazing, present participle of phlegéthein to blaze. See phlegm
• Latin

Phleg′e•thon′tal, Phleg′e•thon′tic, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

Phlegethon / ˈflɛɡɪˌθɒn/ noun

1. a river of fire in Hades

Etymology: 14th Century: from Greek, literally: blazing, from phlegethein to flame, blaze