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.

Roar \Roar\, v. t.
   To cry aloud; to proclaim loudly.

         This last action will roar thy infamy.   --Ford.

Roar \Roar\, n.
   The sound of roaring. Specifically:
   (a) The deep, loud cry of a wild beast; as, the roar of a
       lion.
   (b) The cry of one in pain, distress, anger, or the like.
   (c) A loud, continuous, and confused sound; as, the roar of a
       cannon, of the wind, or the waves; the roar of ocean.

             Arm! arm! it is, it is the cannon's opening roar!
                                                  --Byron.
   (d) A boisterous outcry or shouting, as in mirth.

             Pit, boxes, and galleries were in a constant roar
             of laughter.                         --Macaulay.

Source : WordNet®

roar
     n 1: a deep prolonged loud noise [syn: {boom}, {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}, {roaring}, {yowl}]
     3: the sound made by a lion

roar
     v 1: make a loud noise, as of wind, water, or vehicles; "The wind
          was howling in the trees"; "The water roared down the
          chute" [syn: {howl}]
     2: utter words loudly and forcefully; "`Get out of here,' he
        roared" [syn: {thunder}]
     3: emit long loud cries; "wail in self-pity"; "howl with
        sorrow" [syn: {howl}, {ululate}, {wail}, {yawl}]
     4: act or proceed in a riotous, turbulent, or disorderly way;
        "desperadoes from the hills regularly roared in to take
        over the town"-R.A.Billington
     5: make a loud noise, as of animal; "The bull bellowed" [syn: {bellow}]
     6: laugh unrestrainedly and heartily [syn: {howl}]