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.
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   3. To roar; as the sea in a tempest, or as the wind when
      violent; to make a loud, hollow, continued sound.
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            The bellowing voice of boiling seas.  --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bellowing
    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]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "bellowing":
   abandoned, amok, berserk, carried away, delirious, demoniac,
   distracted, ecstatic, enraptured, feral, ferocious, fierce,
   frantic, frenzied, fulminating, furious, haggard, hog-wild,
   howling, hysterical, in a transport, in hysterics, intoxicated,
   mad, madding, maniac, orgasmic, orgiastic, possessed, rabid,
   raging, ramping, ranting, raving, ravished, roaring, running mad,
   storming, transported, uncontrollable, violent, wild, wild-eyed,
   wild-looking