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.
          [1913 Webster]

                Roaring bulls he would him make to tame.
                                                  --Spenser.
          [1913 Webster]
      (b) To cry loudly, as in pain, distress, or anger.
          [1913 Webster]

                Sole on the barren sands, the suffering chief
                Roared out for anguish, and indulged his grief.
                                                  --Dryden.
          [1913 Webster]

                He scorned to roar under the impressions of a
                finite anger.                     --South.
          [1913 Webster]

   2. To make a loud, confused sound, as winds, waves, passing
      vehicles, a crowd of persons when shouting together, or
      the like.
      [1913 Webster]

            The brazen throat of war had ceased to roar.
                                                  --Milton.
      [1913 Webster]

            How oft I crossed where carts and coaches roar.
                                                  --Gay.
      [1913 Webster]

   3. To be boisterous; to be disorderly.
      [1913 Webster]

            It was a mad, roaring time, full of extravagance.
                                                  --Bp. Burnet.
      [1913 Webster]

   4. To laugh out loudly and continuously; as, the hearers
      roared at his jokes.
      [1913 Webster]

   5. To make a loud noise in breathing, as horses having a
      certain disease. See Roaring, 2.
      [1913 Webster]

   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:

Roar \Roar\, v. t.
   To cry aloud; to proclaim loudly.
   [1913 Webster]

         This last action will roar thy infamy.   --Ford.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]

             Arm! arm! it is, it is the cannon's opening roar!
                                                  --Byron.
       [1913 Webster]
   (d) A boisterous outcry or shouting, as in mirth.
       [1913 Webster]

             Pit, boxes, and galleries were in a constant roar
             of laughter.                         --Macaulay.
       [1913 Webster]

WordNet (r) 3.0 (2006):

roar
    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]
    3: the sound made by a lion
    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: roar, howl]
    2: utter words loudly and forcefully; "`Get out of here,' he
       roared" [syn: thunder, roar]
    3: emit long loud cries; "wail in self-pity"; "howl with sorrow"
       [syn: howl, ululate, wail, roar, yawl, yaup]
    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, roar]
    6: laugh unrestrainedly and heartily [syn: roar, howl]

Moby Thesaurus II by Grady Ward, 1.0:

248 Moby Thesaurus words for "roar":
   Bedlam let loose, assault, attack, barbarize, bark, batter,
   battle cry, bawl, bay, be in stitches, be noisy, bedlam, bell,
   bellow, blare, blast, blat, blate, bleat, blubber, bluster,
   bobbery, boom, booming, brawl, bray, break up, breathe, brouhaha,
   brutalize, burn, burst into laughter, burst out,
   burst out laughing, burst with laughter, bust a gut, butcher, buzz,
   cachinnate, cackle, call, cannonade, carry on, caterwaul, chant,
   charivari, cheer, chirm, chirp, chortle, chuckle, clamor, clangor,
   clap, clatter, commotion, coo, crow, cry, declaim, destroy, din,
   discord, donnybrook, drawl, drunken brawl, dustup, exclaim, flap,
   flute, fracas, free-for-all, gasp, giggle, give tongue, give voice,
   go into convulsions, go on, grimace, groan, growl, growling,
   grumble, grunt, guffaw, ha-ha, hail, halloo, ham, ham it up,
   hammer, hee-haw, hee-hee, hell broke loose, hiss, ho-ho, holler,
   hollo, hoot, horselaugh, howl, hubbub, hue and cry, hullabaloo,
   hurrah, jangle, keen, laugh, laugh it up, laugh outright,
   lay waste, lilt, loot, loud noise, low, maffick, make a noise,
   make a racket, make an uproar, maul, meow, mew, mewl, miaow, moan,
   moo, mug, mumble, murmur, mutter, nearly die laughing, neigh,
   nicker, noise, noise and shouting, out, out-herod Herod, outburst,
   outcry, overact, overdramatize, pandemonium, pant, peal, pillage,
   pipe, pule, racket, rage, raise Cain, raise a clamor, raise hell,
   raise the devil, raise the roof, rallying cry, ramp, rampage, rant,
   rape, rattle, rave, rebound, repercuss, reverberate, rhubarb, riot,
   roar with laughter, roaring, roll, row, ruckus, ruction, ruin,
   rumble, rumpus, sack, savage, screak, scream, screech,
   shake like jelly, shake with laughter, shindy, shivaree, shout,
   shriek, sibilate, sigh, sing, slaughter, snap, snarl, snarling,
   snicker, snigger, snort, sob, sough, sow chaos, split,
   split with laughter, spout, squall, squawk, squeak, squeal, storm,
   tear, tear around, tee-hee, terrorize, throw away, thunder,
   thunderclap, tintamarre, titter, troat, trumpet, tumult, twang,
   ululate, underact, uproar, vandalize, violate, vociferate, wail,
   war cry, war whoop, warble, whicker, whine, whinny, whisper,
   whistle, whoop, whoop it up, wreck, yammer, yap, yawl, yawp, yell,
   yelp, yip, yo-ho, yowl, yuk-yuk