The Collaborative International Dictionary of English v.0.48:

Roar \Roar\, v. i. [imp. & p. p. Roared; p. pr. & vvb. n.
   Roaring.] [OE. roren, raren, AS. r[=a]rian; akin to G.
   r["o]hten, OHG. r[=e]r[=e]n. [root]112.]
   1. To cry with a full, loud, continued sound. Specifically:
      (a) To bellow, or utter a deep, loud cry, as a lion or
          other beast.
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                Roaring bulls he would him make to tame.
                                                  --Spenser.
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      (b) To cry loudly, as in pain, distress, or anger.
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                Sole on the barren sands, the suffering chief
                Roared out for anguish, and indulged his grief.
                                                  --Dryden.
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                He scorned to roar under the impressions of a
                finite anger.                     --South.
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   2. To make a loud, confused sound, as winds, waves, passing
      vehicles, a crowd of persons when shouting together, or
      the like.
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            The brazen throat of war had ceased to roar.
                                                  --Milton.
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            How oft I crossed where carts and coaches roar.
                                                  --Gay.
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   3. To be boisterous; to be disorderly.
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            It was a mad, roaring time, full of extravagance.
                                                  --Bp. Burnet.
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   4. To laugh out loudly and continuously; as, the hearers
      roared at his jokes.
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   5. To make a loud noise in breathing, as horses having a
      certain disease. See Roaring, 2.
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   Roaring boy, a roaring, noisy fellow; -- name given, at the
      latter end Queen Elizabeth's reign, to the riotous fellows
      who raised disturbances in the street. "Two roaring boys
      of Rome, that made all split." --Beau. & Fl.

   Roaring forties (Naut.), a sailor's name for the stormy
      tract of ocean between 40[deg] and 50[deg] north latitude.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Roaring \Roar"ing\, n.
   1. A loud, deep, prolonged sound, as of a large beast, or of
      a person in distress, anger, mirth, etc., or of a noisy
      congregation.
      [1913 Webster]

   2. (Far.) An affection of the windpipe of a horse, causing a
      loud, peculiar noise in breathing under exertion; the
      making of the noise so caused. See Roar, v. i., 5.
      [1913 Webster]

WordNet (r) 3.0 (2006):

roaring
    adv 1: extremely; "roaring drunk"
    adj 1: very lively and profitable; "flourishing businesses"; "a
           palmy time for stockbrokers"; "a prosperous new
           business"; "doing a roaring trade"; "a thriving tourist
           center"; "did a thriving business in orchids" [syn:
           booming, flourishing, palmy, prospering,
           prosperous, roaring, thriving]
    n 1: a deep prolonged loud noise [syn: boom, roar,
         roaring, thunder]
    2: a very loud utterance (like the sound of an animal); "his
       bellow filled the hallway" [syn: bellow, bellowing,
       holla, holler, hollering, hollo, holloa, roar,
       roaring, yowl]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "roaring":
   abandoned, amok, bellowing, berserk, blaring, booming, cannonading,
   carried away, delirious, demoniac, distracted, earsplitting,
   ecstatic, enraptured, feral, ferocious, fierce, frantic, frenzied,
   fulminating, furious, haggard, hog-wild, howling, hysterical,
   in a transport, in hysterics, intoxicated, mad, madding, maniac,
   orgasmic, orgiastic, pealing, piercing, possessed, prospering,
   prosperous, rabid, raging, ramping, ranting, raving, ravished,
   robust, rolling, rumbling, running mad, stentorian, stentorious,
   storming, thrifty, thriving, thundering, thunderlike, thunderous,
   thundery, tonitruant, tonitruous, transported, uncontrollable,
   violent, volleying, wild, wild-eyed, wild-looking