The Collaborative International Dictionary of English v.0.48:

Egregious \E*gre"gious\ (?; 277), a. [L. egregius; lit.,
   separated or chosen from the herd, i. e., distinguished,
   excellent; e out + grex, gregis, herd. See Gregarious.]
   Surpassing; extraordinary; distinguished (in a bad sense); --
   formerly used with words importing a good quality, but now
   joined with words having a bad sense; as, an egregious
   rascal; an egregious ass; an egregious mistake.
   [1913 Webster]

         The egregious impudence of this fellow.  --Bp. Hall.
   [1913 Webster]

         His [Wyclif's] egregious labors are not to be
         neglected.                               --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

egregious
    adj 1: conspicuously and outrageously bad or reprehensible; "a
           crying shame"; "an egregious lie"; "flagrant violation of
           human rights"; "a glaring error"; "gross ineptitude";
           "gross injustice"; "rank treachery" [syn: crying(a),
           egregious, flagrant, glaring, gross, rank]

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "egregious":
   a bit much, abandoned, abominable, absolute, all-embracing,
   all-encompassing, all-out, all-pervading, appalling, arrant,
   astonishing, atrocious, awful, base, beastly, beneath contempt,
   blameworthy, born, boundless, broad-based, brutal, capital,
   classical, clean, clear, complete, comprehensive, congenital,
   conspicuous, consummate, contemptible, crass, decided, deep-dyed,
   definitive, deplorable, despicable, detestable, dire, disgusting,
   downright, dreadful, dyed-in-the-wool, enormous, exaggerated,
   exceptional, excessive, exhaustive, exorbitant, extraordinary,
   extravagant, extreme, fabulous, fancy, fantastic, fetid, filthy,
   flagrant, formidable, foul, fulsome, gigantic, glaring, gluttonous,
   grievous, gross, hateful, heinous, high, horrible, horrid,
   hyperbolic, hypertrophied, immoderate, incontinent, incredible,
   infamous, inordinate, intemperate, intensive, intolerable,
   lamentable, loathsome, lousy, marked, marvelous, monstrous, nasty,
   nefarious, noisome, notable, noteworthy, noticeable, notorious,
   obnoxious, odious, of mark, offensive, omnibus, omnipresent,
   out of bounds, out of sight, out-and-out, outrageous, outright,
   outstanding, overbig, overdeveloped, overgreat, overgrown,
   overlarge, overmuch, overweening, perfect, pervasive, pitiable,
   pitiful, plain, plumb, positive, precious, preposterous, profound,
   pronounced, proper, pure, radical, rank, regrettable, regular,
   remarkable, reprehensible, repulsive, rotten, sad, scandalous,
   schlock, scurvy, shabby, shameful, shattering, sheer, shocking,
   shoddy, signal, sordid, squalid, stark, stark-staring, steep,
   stiff, straight, striking, superior, superlative, surpassing,
   sweeping, terrible, the veriest, thorough, thoroughgoing,
   through-and-through, too bad, too much, total, ubiquitous,
   unbearable, unbridled, unclean, uncommon, unconditional,
   unconscionable, undeniable, undue, unequivocal, universal,
   unmitigated, unqualified, unreasonable, unrelieved, unreserved,
   unrestrained, unrestricted, unspoiled, utter, veritable, vile,
   villainous, wholesale, woeful, wonderful, worst, worthless,
   wretched