The Collaborative International Dictionary of English v.0.48:

Awful \Aw"ful\, a.
   1. Oppressing with fear or horror; appalling; terrible; as,
      an awful scene. "The hour of Nature's awful throes."
      --Hemans.
      [1913 Webster]

   2. Inspiring awe; filling with profound reverence, or with
      fear and admiration; fitted to inspire reverential fear;
      profoundly impressive.
      [1913 Webster]

            Heaven's awful Monarch.               --Milton.
      [1913 Webster]

   3. Struck or filled with awe; terror-stricken. [Obs.]
      [1913 Webster]

            A weak and awful reverence for antiquity. --I.
                                                  Watts.
      [1913 Webster]

   4. Worshipful; reverential; law-abiding. [Obs.]
      [1913 Webster]

            Thrust from the company of awful men. --Shak.
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   5. Frightful; exceedingly bad; great; -- applied intensively;
      as, an awful bonnet; an awful boaster. [Slang]
      [1913 Webster]

   Syn: See Frightful.
        [1913 Webster]

WordNet (r) 3.0 (2006):

awful
    adv 1: used as intensifiers; "terribly interesting"; "I'm awful
           sorry" [syn: terribly, awfully, awful,
           frightfully]
    adj 1: 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]
    2: causing fear or dread or terror; "the awful war"; "an awful
       risk"; "dire news"; "a career or vengeance so direful that
       London was shocked"; "the dread presence of the headmaster";
       "polio is no longer the dreaded disease it once was"; "a
       dreadful storm"; "a fearful howling"; "horrendous explosions
       shook the city"; "a terrible curse" [syn: awful, dire,
       direful, dread(a), dreaded, dreadful, fearful,
       fearsome, frightening, horrendous, horrific,
       terrible]
    3: offensive or even (of persons) malicious; "in a nasty mood";
       "a nasty accident"; "a nasty shock"; "a nasty smell"; "a
       nasty trick to pull"; "Will he say nasty things at my
       funeral?"- Ezra Pound [syn: nasty, awful] [ant: nice]
    4: inspired by a feeling of fearful wonderment or reverence;
       "awed by the silence"; "awful worshippers with bowed heads"
       [syn: awed, awful]
    5: extreme in degree or extent or amount or impact; "in a
       frightful hurry"; "spent a frightful amount of money" [syn:
       frightful, terrible, awful, tremendous]
    6: inspiring awe or admiration or wonder; "New York is an
       amazing city"; "the Grand Canyon is an awe-inspiring sight";
       "the awesome complexity of the universe"; "this sea, whose
       gently awful stirrings seem to speak of some hidden soul
       beneath"- Melville; "Westminster Hall's awing majesty, so
       vast, so high, so silent" [syn: amazing, awe-inspiring,
       awesome, awful, awing]

Moby Thesaurus II by Grady Ward, 1.0:

193 Moby Thesaurus words for "awful":
   Babylonian, Corinthian, abominable, appalling, arrant, astounding,
   atrocious, august, awe-inspiring, awesome, awfully, awing, bad,
   baneful, barbaric, base, beastly, beneath contempt, big, bizarre,
   blameworthy, brutal, contemptible, crazy, damned, deadly, deluxe,
   deplorable, despicable, detestable, dire, direful, disgusting,
   divine, dread, dreaded, dreadful, eerie, egregious, elaborate,
   elegant, enormous, estimable, execrable, extravagant, extremely,
   fancy, fearful, fell, fetid, filthy, fine, flagrant, forbidding,
   formidable, foul, frightful, fulsome, ghastly, ghoulish, glorious,
   grand, grandiose, grave, greatly, grievous, grim, grisly, gross,
   grotesque, gruesome, hateful, heavenly, heinous, hideous, holy,
   honorable, horrendous, horrible, horrid, horrific, horrifying,
   howling, hugely, imposing, impressive, ineffable, inenarrable,
   inexpressible, infamous, inferior, inviolable, inviolate,
   lamentable, loathsome, lousy, luxurious, macabre, magnificent,
   majestic, monstrous, morbid, mortally, moving, much, mysterious,
   nasty, nefarious, noble, noisome, notorious, numinous, obnoxious,
   odious, offensive, ominous, outrageous, palatial, pitiable,
   pitiful, plush, portentous, posh, princely, proud, rank,
   redoubtable, regrettable, religious, repelling, reprehensible,
   repugnant, repulsive, reverend, revolting, ritzy, rotten, rousing,
   sacred, sacrosanct, sad, scandalous, schlock, schrecklich, scurvy,
   serious, shabby, shameful, shocking, shoddy, solemn, sordid,
   spiritual, splendacious, splendid, splendiferous, squalid, stately,
   sumptuous, superb, superfancy, superfine, swank, swanky, swell,
   tasteless, terrible, terribly, terrific, thumping, time-honored,
   too bad, tragic, tremendous, ugly, uncanny, unclean, unpleasant,
   unsightly, unspeakable, untouchable, unutterable, venerable, vile,
   villainous, weird, whacking, whopping, woeful, worshipful, worst,
   worthless, wretched