Source : Webster's Revised Unabridged Dictionary (1913)

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?r?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.

                Roaring bulls he would him make to tame.
                                                  --Spenser.
      (b) To cry loudly, as in pain, distress, or anger.

                Sole on the barren sands, the suffering chief
                Roared out for anguish, and indulged his grief.
                                                  --Dryden.

                He scorned to roar under the impressions of a
                finite anger.                     --South.

   2. To make a loud, confused sound, as winds, waves, passing
      vehicles, a crowd of persons when shouting together, or
      the like.

            The brazen throat of war had ceased to roar.
                                                  --Milton.

            How oft I crossed where carts and coaches roar.
                                                  --Gay.

   3. To be boisterous; to be disorderly.

            It was a mad, roaring time, full of extravagance.
                                                  --Bp. Burnet.

   4. To laugh out loudly and continuously; as, the hearers
      roared at his jokes.

   5. To make a loud noise in breathing, as horses having a
      certain disease. See {Roaring}, 2.

   {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.

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.

   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.

Source : WordNet®

roaring
     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}, {thriving}]
     2: loud enough to cause (temporary) hearing loss [syn: {deafening},
         {earsplitting}, {thunderous}, {thundery}]
     n 1: a deep prolonged loud noise [syn: {boom}, {roar}, {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}, {yowl}]
     adv : extremely; "roaring drunk"