Source : Webster's Revised Unabridged Dictionary (1913)

Infernal \In*fer"nal\, n.
   An inhabitant of the infernal regions; also, the place
   itself. [Obs.] --Drayton.

Infernal \In*fer"nal\, a. [F. infernal, L. infernalis, fr.
   infernus that which lies beneath, the lower. See {Inferior}.]
   1. Of or pertaining to or suitable for the lower regions,
      inhabited, according to the ancients, by the dead;
      pertaining to Pluto's realm of the dead, the Tartarus of
      the ancients.

            The Elysian fields, the infernal monarchy. --Garth.

   2. Of or pertaining to, resembling, or inhabiting, hell;
      suitable for hell, or to the character of the inhabitants
      of hell; hellish; diabolical; as, infernal spirits, or
      conduct.

            The instruments or abettors in such infernal
            dealings.                             --Addison.

   {Infernal machine}, a machine or apparatus maliciously
      designed to explode, and destroy life or property.

   {Infernal stone} (lapis infernalis), lunar caustic; formerly
      so called. The name was also applied to caustic potash.

   Syn: Tartarean; Stygian; hellish; devilish; diabolical;
        satanic; fiendish; malicious.

Source : WordNet®

infernal
     n : an inhabitant of hell; "his roar made the infernals quake"

infernal
     adj 1: characteristic of or resembling hell; "infernal heat and
            noise"
     2: extremely evil or cruel; expressive of cruelty or befitting
        hell; "something demonic in him--something that could be
        cruel"; "fires lit up a diabolic scene"; "diabolical
        sorcerers under the influence of devils"; "a fiendish
        despot"; "hellish torture"; "infernal instruments of war";
        "satanic cruelty"; "unholy grimaces" [syn: {demonic}, {diabolic},
         {diabolical}, {fiendish}, {hellish}, {satanic}, {unholy}]
     3: expletives used informally as intensifiers; "he's a blasted
        idiot"; "it's a blamed shame"; "a blame cold winter"; "not
        a blessed dime"; "I'll be damned (or blessed or darned or
        goddamned) if I'll do any such thing"; "he's a damn (or
        goddam or goddamned) fool"; "a deuced idiot"; "tired or
        his everlasting whimpering"; "an infernal nuisance" [syn:
        {blasted}, {blame}, {blamed}, {blessed}, {damn}, {damned},
         {darned}, {deuced}, {everlasting}, {goddam}, {goddamn}, {goddamned}]
     4: relating to or inhabiting hell; "his infernal majesty";
        "infernal fires"; "infernal punishments"
     5: being of a lower world of the dead; "infernal regions" [ant:
         {supernal}]