The Collaborative International Dictionary of English v.0.48:

Inferno \In*fer"no\, n. [It. See Infernal.]
   1. The infernal regions; hell.
      [Webster 1913 Suppl.]

   2. Hence: A raging fire.
      [PJC]

            At each sudden explosion in the inferno below they
            sprang back from the brink [of the volcanic crater].
                                                  --D. C.
                                                  Worcester.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

inferno
    n 1: any place of pain and turmoil; "the hell of battle"; "the
         inferno of the engine room"; "when you're alone Christmas
         is the pits"; [syn: hell, hell on earth, hellhole,
         snake pit, the pits, inferno]
    2: a very intense and uncontrolled fire [syn: conflagration,
       inferno]
    3: (Christianity) the abode of Satan and the forces of evil;
       where sinners suffer eternal punishment; "Hurl'd
       headlong...To bottomless perdition, there to dwell"- John
       Milton; "a demon from the depths of the pit"; "Hell is paved
       with good intentions"-Dr. Johnson [syn: Hell, perdition,
       Inferno, infernal region, nether region, pit] [ant:
       Heaven]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "inferno":
   Abaddon, Gehenna, Hades, Naraka, Pandemonium, Sheol, Tophet,
   Torrid Zone, abyss, avichi, blazes, conflagration, equator,
   furnace, hades, hell, holocaust, infernal regions, jahannan, limbo,
   lower world, nether world, netherworld, oven, perdition, pit,
   place of torment, purgatory, shades below, steam bath, subtropics,
   the abyss, the bottomless pit, the grave, the pit, tropics,
   underworld