The Collaborative International Dictionary of English v.0.48:

Howl \Howl\, v. i. [imp. & p. p. Howled; p. pr. & vb. n.
   Howling.] [OE. houlen, hulen; akin to D. huilen, MHG.
   hiulen, hiuweln, OHG. hiuwil[=o]n to exult, h?wo owl, Dan.
   hyle to howl.]
   1. To utter a loud, protracted, mournful sound or cry, as
      dogs and wolves often do.
      [1913 Webster]

            And dogs in corners set them down to howl.
                                                  --Drayton.
      [1913 Webster]

            Methought a legion of foul fiends
            Environ'd me about, and howled in my ears. --Shak.
      [1913 Webster]

   2. To utter a sound expressive of distress; to cry aloud and
      mournfully; to lament; to wail.
      [1913 Webster]

            Howl ye, for the day of the Lord is at hand. --Is.
                                                  xiii. 6.
      [1913 Webster]

   3. To make a noise resembling the cry of a wild beast.
      [1913 Webster]

            Wild howled the wind.                 --Sir W.
                                                  Scott.
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   Howling monkey. (Zool.) See Howler, 2.

   Howling wilderness, a wild, desolate place inhabited only
      by wild beasts. --Deut. xxxii. 10.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Howl \Howl\, v. t.
   To utter with outcry. "Go . . . howl it out in deserts."
   --Philips.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Howl \Howl\, n.
   1. The protracted, mournful cry of a dog or a wolf, or other
      like sound.
      [1913 Webster]

   2. A prolonged cry of distress or anguish; a wail.
      [1913 Webster]

WordNet (r) 3.0 (2006):

howl
    n 1: a long loud emotional utterance; "he gave a howl of pain";
         "howls of laughter"; "their howling had no effect" [syn:
         howl, howling, ululation]
    2: the long plaintive cry of a hound or a wolf
    3: a loud sustained noise resembling the cry of a hound; "the
       howl of the wind made him restless"
    v 1: emit long loud cries; "wail in self-pity"; "howl with
         sorrow" [syn: howl, ululate, wail, roar, yawl,
         yaup]
    2: cry loudly, as of animals; "The coyotes were howling in the
       desert" [syn: howl, wrawl, yammer, yowl]
    3: 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]
    4: laugh unrestrainedly and heartily [syn: roar, howl]

Moby Thesaurus II by Grady Ward, 1.0:

236 Moby Thesaurus words for "howl":
   Bedlam let loose, air a grievance, animal noise, bark, barking,
   battle cry, bawl, bay, bedlam, beef, beefing, bell, bellow,
   bellyache, bellyaching, birdcall, bitch, bitching, blare, blast,
   blat, blate, bleat, bobbery, boggle, boycott, brawl, bray,
   brouhaha, call, call in question, caterwaul, challenge, charivari,
   cheer, chirm, clamor, clang, clangor, clap, clatter, commotion,
   complain, complaining, complaint, compunction, crab, creak, croak,
   cry, cry out, cry out against, demonstrate, demonstrate against,
   demonstration, demur, demurrer, destructive criticism, din,
   discord, dispute, dissent, dolorous tirade, donnybrook,
   drunken brawl, dustup, enter a protest, exception, expostulate,
   expostulation, faultfinding, flap, fracas, free-for-all, fret,
   fret and fume, fuss, give tongue, give voice, grievance,
   grievance committee, gripe, griping, groan, groaning, grouch,
   grouse, grousing, growl, grumble, grumbling, grunt, hail, halloo,
   hell broke loose, holler, hollo, hoot, howling, hubbub,
   hue and cry, hullabaloo, hurrah, indignation meeting, jangle,
   jeremiad, keen, kick, kicking, lament, lodge a complaint,
   loud noise, low, make an outcry, march, mating call, meow, mew,
   mewl, miaow, moan, moo, murmur, murmuring, mutter, neigh, nicker,
   noise, noise and shouting, nonviolent protest, note, object,
   objection, outcry, pandemonium, panic, peeve, peevishness,
   pet peeve, petulance, picket, picketing, pipe, plaint, planctus,
   press objections, protest, protest demonstration, protestation,
   pule, qualm, querulousness, racket, raise a howl, rally,
   rallying cry, rattle, register a complaint, remonstrance,
   remonstrate, remonstration, rhubarb, roar, row, ruckus, ruction,
   rumble, rumpus, scolding, screak, scream, screech, scruple, shindy,
   shivaree, shout, shriek, shrill, sidesplitter, sigh, sing, sit in,
   sit-in, skirl, skreigh, snarl, sniping, sob, sough, squall, squawk,
   squawking, squeak, squeal, state a grievance, stridulation, strike,
   take on, teach in, teach-in, thunder, thunderclap, tintamarre,
   tirade, troat, tumult, ululate, ululation, uproar, wail,
   wail of woe, wailing, war cry, war whoop, whicker, whimper, whine,
   whining, whinny, whisper, whistle, whoop, woodnote, wrawl, yammer,
   yap, yapping, yawl, yawp, yell, yell bloody murder, yelp, yelping,
   yip, yo-ho, yowl