The Collaborative International Dictionary of English v.0.48:

Brutal \Bru"tal\, a. [Cf. F. brutal. See Brute, a.]
   1. Of or pertaining to a brute; as, brutal nature. "Above the
      rest of brutal kind." --Milton.
      [1913 Webster]

   2. Like a brute; savage; cruel; inhuman; brutish; unfeeling;
      merciless; gross; as, brutal manners. "Brutal
      intemperance." --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

brutal
    adj 1: (of persons or their actions) able or disposed to inflict
           pain or suffering; "a barbarous crime"; "brutal
           beatings"; "cruel tortures"; "Stalin's roughshod
           treatment of the kulaks"; "a savage slap"; "vicious
           kicks" [syn: barbarous, brutal, cruel, fell,
           roughshod, savage, vicious]
    2: harsh; "the brutal summer sun"; "a brutal winter" [syn:
       brutal, unrelenting]
    3: resembling a beast; showing lack of human sensibility;
       "beastly desires"; "a bestial nature"; "brute force"; "a dull
       and brutish man"; "bestial treatment of prisoners" [syn:
       beastly, bestial, brute(a), brutish, brutal]
    4: disagreeably direct and precise; "he spoke with brutal
       honesty"

Moby Thesaurus II by Grady Ward, 1.0:

242 Moby Thesaurus words for "brutal":
   Adamic, Circean, Draconian, Gothic, Herculean, Neanderthal,
   Tartarean, abominable, abstruse, animal, animalian, animalic,
   animalistic, anthropophagous, arduous, arrant, atrocious, awful,
   baneful, barbarian, barbaric, barbarous, base, beastlike, beastly,
   beneath contempt, bestial, bitter, blameworthy, bloodthirsty,
   bloody, bloody-minded, bodily, boorish, brutalized, brute,
   brutelike, brutish, cannibalistic, carnal, carnal-minded, coarse,
   cold-blooded, complex, contemptible, crass, critical, crude, cruel,
   cruel-hearted, deadly, death-bringing, deathful, deathly, delicate,
   demanding, demoniac, demoniacal, deplorable, despicable,
   destructive, detestable, devilish, diabolic, difficile, difficult,
   dire, disgusting, dreadful, dumb, earthy, egregious, enormous,
   exacting, fallen, fatal, fell, feral, ferine, ferocious, fetid,
   fiendish, fiendlike, fierce, filthy, flagrant, fleshly, formidable,
   foul, fulsome, grievous, gross, hairy, hard, hard-earned,
   hard-fought, harsh, hateful, heartless, heinous, hellish, horrible,
   horrid, ill-bred, ill-mannered, impolite, inclement, infamous,
   infernal, inhuman, inhumane, insensitive, instinctive, instinctual,
   intemperate, internecine, intricate, jawbreaking, kill-crazy,
   killing, knotted, knotty, laborious, lamentable, lapsed, lethal,
   loathsome, lousy, malign, malignant, material, materialistic, mean,
   merciless, mindless, monstrous, mortal, murderous, nasty,
   nefarious, no picnic, noisome, noncivilized, nonrational,
   nonspiritual, not easy, notorious, obnoxious, odious, offensive,
   operose, orgiastic, outlandish, outrageous, pernicious, physical,
   pitiable, pitiful, pitiless, postlapsarian, primitive, rank,
   regrettable, remorseless, reprehensible, repulsive, rigorous,
   rotten, rough, rough-and-ready, rude, rugged, rustic, ruthless,
   sad, sadistic, sanguinary, sanguineous, satanic, savage,
   scandalous, schlock, scurvy, set with thorns, severe, shabby,
   shameful, sharkish, shocking, shoddy, slavering, sordid, spiny,
   squalid, steep, strenuous, subhuman, swinish, tameless, terrible,
   thorny, ticklish, toilsome, too bad, tough, tricky, troglodytic,
   truculent, unchristian, uncivil, uncivilized, unclean, uncombed,
   uncouth, uncultivated, uncultured, unfeeling, ungentle, unhuman,
   unkempt, unkind, unlicked, unpolished, unrefined, unspiritual,
   unsympathetic, untamed, uphill, vicious, vile, villainous,
   virulent, wicked, wild, woeful, wolfish, worst, worthless,
   wretched, zoic, zooidal, zoologic