The Collaborative International Dictionary of English v.0.48:

Enormous \E*nor"mous\, a. [L. enormis enormous, out of rule; e
   out + norma rule: cf. F. ['e]norme. See Normal.]
   1. Exceeding the usual rule, norm, or measure; out of due
      proportion; inordinate; abnormal. "Enormous bliss."
      --Milton. "This enormous state." --Shak. "The hoop's
      enormous size." --Jenyns.
      [1913 Webster]

            Wallowing unwieldy, enormous in their gait.
                                                  --Milton.
      [1913 Webster]

   2. Exceedingly wicked; outrageous; atrocious; monstrous; as,
      an enormous crime.
      [1913 Webster]

            That detestable profession of a life so enormous.
                                                  --Bale.

   Syn: Huge; vast; immoderate; immense; excessive; prodigious;
        monstrous.

   Usage: -- Enormous, Immense, Excessive. We speak of a
          thing as enormous when it overpasses its ordinary law
          of existence or far exceeds its proper average or
          standard, and becomes -- so to speak -- abnormal in
          its magnitude, degree, etc.; as, a man of enormous
          strength; a deed of enormous wickedness. Immense
          expresses somewhat indefinitely an immeasurable
          quantity or extent. Excessive is applied to what is
          beyond a just measure or amount, and is always used in
          an evil; as, enormous size; an enormous crime; an
          immense expenditure; the expanse of ocean is immense.
          "Excessive levity and indulgence are ultimately
          excessive rigor." --V. Knox. "Complaisance becomes
          servitude when it is excessive." --La Rochefoucauld
          (Trans).
          [1913 Webster]

WordNet (r) 3.0 (2006):

enormous
    adj 1: extraordinarily large in size or extent or amount or
           power or degree; "an enormous boulder"; "enormous
           expenses"; "tremendous sweeping plains"; "a tremendous
           fact in human experience; that a whole civilization
           should be dependent on technology"- Walter Lippman; "a
           plane took off with a tremendous noise" [syn: enormous,
           tremendous]

Moby Thesaurus II by Grady Ward, 1.0:

151 Moby Thesaurus words for "enormous":
   Atlantean, Brobdingnagian, Cyclopean, Gargantuan, Herculean,
   Homeric, a bit much, abandoned, abominable, abysmal, amplitudinous,
   arrant, astronomic, astronomical, atrocious, awesome, awful, base,
   beastly, beneath contempt, blameworthy, boundless, brutal, bulky,
   colossal, contemptible, cosmic, deplorable, despicable, detestable,
   dire, disgusting, dreadful, egregious, elephantine, epic,
   exaggerated, excessive, exorbitant, extensive, extravagant,
   extreme, fabulous, fancy, fetid, filthy, flagrant, foul, fulsome,
   galactic, gargantuan, giant, giantlike, gigantic, gluttonous,
   grievous, gross, hateful, heinous, heroic, high, horrible, horrid,
   huge, hyperbolic, hypertrophied, immeasurable, immense, immoderate,
   incontinent, infamous, infinite, inordinate, intemperate, jumbo,
   king-size, lamentable, large, loathsome, lousy, mammoth, massive,
   massy, mighty, monster, monstrous, monumental, mountainous, nasty,
   nefarious, noisome, notorious, obnoxious, odious, offensive,
   out of bounds, out of sight, outrageous, outsize, overbig,
   overdeveloped, overgreat, overgrown, overlarge, overmuch,
   overweening, pitiable, pitiful, prodigious, profound, rank,
   regrettable, reprehensible, repulsive, rotten, sad, scandalous,
   schlock, scurvy, shabby, shameful, shocking, shoddy, sizable,
   sordid, spacious, squalid, steep, stiff, stupendous, terrible,
   titanic, too bad, too much, towering, tremendous, unbridled,
   unclean, unconscionable, undue, unreasonable, unrestrained, vast,
   vile, villainous, voluminous, weighty, woeful, worst, worthless,
   wretched