The Collaborative International Dictionary of English v.0.48:

Atrocious \A*tro"cious\, a. [L. atrox, atrocis, cruel, fierce:
   cf. F. atroce.]
   1. Extremely heinous; full of enormous wickedness; as,
      atrocious guilt or deeds.
      [1913 Webster]

   2. Characterized by, or expressing, great atrocity.
      [1913 Webster]

            Revelations . . . so atrocious that nothing in
            history approaches them.              --De Quincey.
      [1913 Webster]

   3. Very grievous or violent; terrible; as, atrocious
      distempers. [Obs.] --Cheyne.
      [1913 Webster]

   Syn: Atrocious, Flagitious, Flagrant.

   Usage: Flagitious points to an act as grossly wicked and
          vile; as, a flagitious proposal. Flagrant marks the
          vivid impression made upon the mind by something
          strikingly wrong or erroneous; as, a flagrant
          misrepresentation; a flagrant violation of duty.
          Atrocious represents the act as springing from a
          violent and savage spirit. If Lord Chatham, instead of
          saying "the atrocious crime of being a young man," had
          used either of the other two words, his irony would
          have lost all its point, in his celebrated reply to
          Sir Robert Walpole, as reported by Dr. Johnson.
          [1913 Webster] -- A*tro"cious*ly, adv. --
          A*tro"cious*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

atrocious
    adj 1: shockingly brutal or cruel; "murder is an atrocious
           crime"; "a grievous offense against morality"; "a
           grievous crime"; "no excess was too monstrous for them to
           commit" [syn: atrocious, flagitious, grievous,
           monstrous]
    2: exceptionally bad or displeasing; "atrocious taste";
       "abominable workmanship"; "an awful voice"; "dreadful
       manners"; "a painful performance"; "terrible handwriting";
       "an unspeakable odor came sweeping into the room" [syn:
       atrocious, abominable, awful, dreadful, painful,
       terrible, unspeakable]
    3: provoking horror; "an atrocious automobile accident"; "a
       frightful crime of decapitation"; "an alarming, even
       horrifying, picture"; "war is beyond all words horrible"-
       Winston Churchill; "an ugly wound" [syn: atrocious,
       frightful, horrifying, horrible, ugly]

Moby Thesaurus II by Grady Ward, 1.0:

261 Moby Thesaurus words for "atrocious":
   Draconian, Tartarean, aberrant, abject, abnormal, abominable,
   abusive, acute, afflictive, agonizing, animal, anthropophagous,
   appalling, arrant, atrocious, awful, backhand, backhanded, bad,
   baneful, barbaric, barbarous, base, beastly, beggarly,
   beneath contempt, bestial, biting, black, blamable, blameworthy,
   bloodthirsty, bloody, bloody-minded, brutal, brutalized, brute,
   brutish, calumnious, cannibalistic, cheesy, contemptible,
   contumelious, cramping, criminal, cruel, cruel-hearted, crummy,
   crying, damnable, dark, debased, degraded, degrading, delinquent,
   demoniac, demoniacal, deplorable, depraved, desperate, despicable,
   detestable, deviant, devilish, diabolic, dire, dirty, disgraceful,
   disgusting, displeasing, distasteful, distressing, dreadful,
   egregious, enormous, evil, excruciating, execrable, fell, feral,
   ferine, ferocious, fetid, fiendish, fiendlike, fierce, filthy,
   flagitious, flagrant, foul, frightful, fulsome, ghastly, glaring,
   gnawing, grave, grievous, grim, griping, grisly, gross, gruesome,
   hard, hardly the thing, harrowing, harsh, hateful, heinous,
   hellish, hideous, horrendous, horrible, horrid, horrific,
   horrifying, humiliating, hurtful, hurting, icky, ignominious,
   illegal, improper, inappropriate, incorrect, indecorous, infamous,
   infernal, inhuman, inhumane, iniquitous, insolent, insulting,
   kill-crazy, knavish, lamentable, left-handed, little, loathsome,
   lousy, low, low-down, lumpen, malign, malignant, mangy, mean,
   measly, merciless, miserable, monstrous, murderous, nasty, naughty,
   nefarious, noisome, noncivilized, not done, not the thing,
   notorious, obnoxious, obscene, odious, off-base, off-color,
   offensive, out-of-line, outrageous, painful, paltry, paroxysmal,
   peccant, petty, piercing, pitiable, pitiful, pitiless, poignant,
   poky, poor, pungent, racking, rank, regrettable, reprehensible,
   reprobate, rotten, ruthless, sacrilegious, sad, sadistic,
   sanguinary, sanguineous, satanic, savage, scabby, scandalous,
   schlock, scrubby, scruffy, scummy, scurrile, scurrilous, scurvy,
   severe, shabby, shameful, shameless, sharkish, sharp, shocking,
   shoddy, shooting, sickening, sinful, slavering, small, sordid,
   spasmatic, spasmic, spasmodic, squalid, stabbing, stinging,
   subhuman, tameless, terrible, too bad, tormenting, torturous,
   tragic, truculent, unchristian, uncivilized, unclean, undue, unfit,
   unfitting, unforgivable, ungentle, unhuman, unlawful,
   unmentionable, unpardonable, unrighteous, unseemly, unspeakable,
   unsuitable, untamed, unworthy, vicious, vile, villainous, wicked,
   wild, woeful, wolfish, worst, worthless, wretched, wrong,
   wrongful