The Collaborative International Dictionary of English v.0.48:

Vociferous \Vo*cif"er*ous\, a. [Cf. F. vocif[`e]re.]
   Making a loud outcry; clamorous; noisy; as, vociferous
   heralds. -- Vo*cif"er*ous*ly, adv. -- Vo*cif"er*ous*ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vociferous
    adj 1: conspicuously and offensively loud; given to vehement
           outcry; "blatant radios"; "a clamorous uproar"; "strident
           demands"; "a vociferous mob" [syn: blatant, clamant,
           clamorous, strident, vociferous]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "vociferous":
   bawling, blaring, blatant, blatting, blustering, boanergean,
   boisterous, brassy, brawling, brazen, clamant, clamorous,
   clamoursome, clanging, clangorous, clattery, crying, loudmouthed,
   mafficking, noiseful, noisy, obstreperous, openmouthed, rackety,
   rip-roaring, rowdy, screaming, shouting, strepitant, strepitous,
   tumultuous, turbulent, uproarious, vociferant, vociferating,
   yammering, yapping, yelling, yelping