The Collaborative International Dictionary of English v.0.48:

Bellow \Bel"low\, v. i. [imp. & p. p. Bellowed; p. pr. & vb.
   n. Bellowing.] [OE. belwen, belowen, AS. bylgean, fr.
   bellan; akin to G. bellen, and perh. to L. flere to weep,
   OSlav. bleja to bleat, Lith. balsas voice. Cf. Bell, n. &
   v., Bawl, Bull.]
   1. To make a hollow, loud noise, as an enraged bull.
      [1913 Webster]

   2. To bowl; to vociferate; to clamor. --Dryden.
      [1913 Webster]

   3. To roar; as the sea in a tempest, or as the wind when
      violent; to make a loud, hollow, continued sound.
      [1913 Webster]

            The bellowing voice of boiling seas.  --Dryden.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bellow \Bel"low\, v. t.
   To emit with a loud voice; to shout; -- used with out. "Would
   bellow out a laugh." --Dryden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bellow \Bel"low\, n.
   A loud resounding outcry or noise, as of an enraged bull; a
   roar.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bellow
    n 1: 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]
    2: United States author (born in Canada) whose novels influenced
       American literature after World War II (1915-2005) [syn:
       Bellow, Saul Bellow, Solomon Bellow]
    v 1: shout loudly and without restraint [syn: bawl, bellow]
    2: make a loud noise, as of animal; "The bull bellowed" [syn:
       bellow, roar]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "bellow":
   bark, battle cry, bawl, bay, be angry, be excitable, bell,
   bellow out, blare, blat, blate, bleat, blow a gasket, blow up,
   blubber, bluster, boom, bray, breathe, buzz, cackle, call,
   call out, catch fire, catch the infection, caterwaul, chant, cheer,
   chirp, clamor, come apart, coo, crow, cry, cry out, drawl,
   excite easily, exclaim, explode, fire up, flame up, flare up,
   flash up, flip, flute, gasp, get excited, give tongue, give voice,
   go into hysterics, growl, grunt, hail, halloo, have a tantrum,
   hiss, hit the ceiling, holler, holler out, hollo, hoot, howl,
   hurrah, keen, lilt, low, make an outcry, make an uproar, meow, mew,
   mewl, miaow, moo, mumble, murmur, mutter, neigh, nicker, outcry,
   pant, pipe, pipe up, pule, rage, raise a clamor, rallying cry,
   ramp, rant, rant and rave, rave, roar, rout, rumble,
   run a temperature, screak, scream, screech, seethe, shout,
   shout out, shriek, sibilate, sigh, sing, sing out, smolder, snap,
   snarl, snort, sob, squall, squawk, squeak, squeal, storm,
   take fire, thunder, troat, trumpet, turn a hair, twang, ululate,
   vociferate, wail, war cry, war whoop, warble, whicker, whine,
   whinny, whisper, whoop, yammer, yap, yawl, yawp, yell, yell out,
   yelp, yip, yo-ho, yowl