infernal UK /ɪnˈfɜː(ɹ)nəl/US /ɪnˈfɝnəl/adjective 5noun 1forms 3 adjective5 •Of or relating to hell, or the world of the dead; hellish.He proffered a pact to Satan, calling upon the Fiend and working himself into a frenzy - but his infernal majesty failed to respond. — 1965 •Very annoying; damned.As I had to put up with the patronage and the lecturings, and the eyeglass of that infernal old woman, […] — 1905 •Diabolical or fiendish.Th' infernal Serpent; he it was, whose guile Stird up with Envy and Revenge, deceiv'd The Mother of Mankind — 1674 •Of or relating to a fire or inferno. •Stygian, gloomy. noun1 •An inhabitant of the infernal regions, a demon. formsinfernals · more infernal · most infernal