infernal

adj

1. 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.”

2. (broadly)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”

   “the instruments or abettors in such infernal dealings”

5. Very annoying; damned.

   “As I had to put up with the patronage and the lecturings, and the eyeglass of that infernal old woman, […]”

   “When are you ever going to learn to mind your own infernal business?”

noun

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