infernal

Etymology

From Middle French infernal, from Medieval Latin infernalis, from Latin īnfernus, from īnferum (“netherworld, underworld, hell”).

adj

1. Of or relating to hell, or the world of the dead; hellish.
2. (by extension) Of or relating to a fire or inferno.
3. Stygian, gloomy.
4. Diabolical or fiendish.
   Th' infernal Serpent; he it was, whose guile Stird up with Envy and Revenge, deceiv'd The Mother of Mankind 1674, John Milton, Paradise Lost, Book I, lines 34–36
5. (as an expletive) Very annoying; damned.
   As I had to put up with the patronage and the lecturings, and the eyeglass of that infernal old woman, […] 1905, Bram Stoker, The Man
   When are you ever going to learn to mind your own infernal business? 1982, Sharon Green, The Warrior Within, page 10

noun

1. An inhabitant of the infernal regions, a demon.