The Collaborative International Dictionary of English v.0.48:

Murderous \Mur"der*ous\, a.
   Of or pertaining to murder; characterized by, or causing,
   murder or bloodshed; having the purpose or quality of murder;
   bloody; sanguinary; as, the murderous king; murderous rapine;
   murderous intent; a murderous assault. "Murderous coward."
   --Shak. -- Mur"der*ous*ly, adv.
   [1913 Webster]

   Syn: Bloody; sanguinary; bloodguilty; bloodthirsty; fell;
        savage; cruel.
        [1913 Webster]

WordNet (r) 3.0 (2006):

murderous
    adj 1: characteristic of or capable of or having a tendency
           toward killing another human being ; "a homicidal rage";
           "murderous thugs" [syn: homicidal, murderous]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "murderous":
   Draconian, Tartarean, animal, anthropophagous, arduous, atrocious,
   barbaric, barbarous, beastly, bestial, bloodthirsty, bloody,
   bloody-minded, brutal, brutalized, brute, brutish, cannibalistic,
   cruel, cruel-hearted, cutthroat, deadly, deathly, demoniac,
   demoniacal, destructive, devastating, devilish, diabolic,
   difficult, exhausting, fatal, fell, feral, ferine, ferocious,
   fiendish, fiendlike, fierce, gory, harrowing, hellish, homicidal,
   infernal, inhuman, inhumane, intolerable, kill-crazy, killing,
   lethal, malign, malignant, merciless, mortal, murdering,
   noncivilized, pitiless, red-handed, rigorous, ruinous, ruthless,
   sadistic, sanguinary, sanguine, sanguineous, satanic, savage,
   self-destructive, sharkish, slaughterous, slavering, strenuous,
   stressful, subhuman, suicidal, tameless, truculent, unbearable,
   unchristian, uncivilized, ungentle, unhuman, untamed, vicious,
   wild, wolfish