phleg·e·thon·tal \|flegə|thäntəl, -ejə|-\adjective orphleg·e·thon·tic\-tik\ Usage: usually capitalized Etymology: Latin phlegethontis phlegethontal (from Phlegethon, principal river of Hades that ran with fire instead of water, from Greek Phlegethōn, from phlegethein to blaze, from phlegein to burn) + English -al or -ic archaic: of, relating to, or resembling a river of fire : burning