The Collaborative International Dictionary of English v.0.48:

Beastly \Beast"ly\ (b[=e]st"l[y^]), a.
   1. Pertaining to, or having the form, nature, or habits of, a
      beast.
      [1913 Webster]

            Beastly divinities and droves of gods. --Prior.
      [1913 Webster]

   2. Characterizing the nature of a beast; contrary to the
      nature and dignity of man; brutal; filthy.
      [1913 Webster]

            The beastly vice of drinking to excess. --Swift.
      [1913 Webster]

   3. Abominable; as, beastly weather. [Colloq. Eng.]
      [1913 Webster]

   Syn: Bestial; brutish; irrational; sensual; degrading.
        [1913 Webster]

WordNet (r) 3.0 (2006):

beastly
    adv 1: in a beastly manner; "she behaved beastly toward her
           mother-in-law"
    adj 1: very unpleasant; "hellish weather"; "stop that god-awful
           racket" [syn: beastly, hellish, god-awful]
    2: 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]

Moby Thesaurus II by Grady Ward, 1.0:

205 Moby Thesaurus words for "beastly":
   Adamic, Circean, Draconian, Tartarean, abhorrent, abominable,
   abrupt, aggressive, animal, animalian, animalic, animalistic,
   anthropophagous, appalling, arrant, atrocious, awful, baneful,
   barbaric, barbarous, base, bearish, beastlike, below contempt,
   beneath contempt, bestial, blameworthy, bloodthirsty, bloody,
   bloody-minded, bluff, blunt, bodily, boorish, brash, brusque,
   brutal, brutalized, brute, brutelike, brutish, cannibalistic,
   carnal, carnal-minded, cavalier, churlish, coarse, contemptible,
   crude, cruel, cruel-hearted, crusty, curt, demoniac, demoniacal,
   deplorable, despicable, detestable, devilish, diabolic, dire,
   dirty, disagreeable, disgusting, dreadful, dumb, earthy, egregious,
   enormous, execrable, fallen, fell, feral, ferine, ferocious, fetid,
   fiendish, fiendlike, fierce, filthy, flagrant, fleshly, forbidding,
   foul, fulsome, ghastly, grievous, grim, gross, gruff, harsh,
   hateful, heinous, hellish, hideous, hoggish, horrendous, horrible,
   horrid, horrific, horrifying, ignoble, infamous, infernal, inhuman,
   inhumane, instinctive, instinctual, intolerable, lamentable,
   lapsed, loathsome, lousy, malodorous, material, materialistic,
   mephitic, miasmal, miasmic, mindless, monstrous, murderous, nasty,
   nauseating, nefarious, noisome, nonrational, nonspiritual,
   notorious, noxious, objectionable, obnoxious, obscene, odious,
   offensive, orgiastic, outrageous, physical, piggish, pitiable,
   pitiful, postlapsarian, rank, rebarbative, regrettable, repellent,
   reprehensible, repugnant, repulsive, revolting, rotten, rough,
   rude, ruthless, sad, sadistic, sanguinary, sanguineous, satanic,
   savage, scandalous, schlock, scurvy, severe, shabby, shameful,
   sharkish, sharp, shocking, shoddy, short, sickening, slavering,
   snippy, sordid, squalid, stinking, subhuman, surly, swinish,
   terrible, too bad, tragic, truculent, unchristian, uncivil,
   uncivilized, unclean, uncultivated, unhuman, unpleasant, unrefined,
   unspeakable, unspiritual, vicious, vile, villainous, woeful,
   wolfish, worst, worthless, wretched, zoic, zooidal, zoologic