infernal (adj.)

late 14c., "of or pertaining to the underworld," (ancient Tartarus, the sunless abode of the dead, or the Christian Hell), from Old French enfernal, infernal "of Hell, hellish" (12c.), from Late Latin infernalis "of or belonging to the lower regions," from infernus "hell" (Ambrose), in classical Latin "the lower (world)," noun use of infernus "lower, lying beneath, underground, of the lower regions," from infra "below" (see infra-).

Pluto was infernus rex, and Latin inferi meant "the inhabitants of the infernal regions, the dead." Association of the word with fire and heat is via the Christian conception of Hell. Meaning "devilish, hateful" is from early 15c.; meaning "suitable for or appropriate to Hell" is from c. 1600. As a name of Hell, or a word for things which resemble it, the Italian form inferno has been used in English since 1834, via Dante. Related: Infernally.

Definitions of infernal
infernal (adj.)
characteristic of or resembling Hell;
infernal punishment
infernal noise
infernal (adj.)
extremely evil or cruel; expressive of cruelty or befitting hell;
infernal instruments of war
infernal (adj.)
expletives used informally as intensifiers;
an infernal nuisance
Synonyms: blasted / blame / blamed / blessed / damn / damned / darned / deuced / goddam / goddamn / goddamned
infernal (adj.)
of or pertaining to or characteristic of a very uncontrolled and intense fire;
infernal heat
infernal (adj.)
being of the underworld;
infernal regions
infernal (n.)
an inhabitant of Hell;
his roar made the infernals quake