Source : Webster's Revised Unabridged Dictionary (1913)

Fantastic \Fan*tas"tic\, a. [F. fantastique, fr. Gr. ???????????
   able to represent, fr. ????????? to make visible. See
   {Fancy}.]
   1. Existing only in imagination; fanciful; imaginary; not
      real; chimerical.

   2. Having the nature of a phantom; unreal. --Shak.

   3. Indulging the vagaries of imagination; whimsical; full of
      absurd fancies; capricious; as, fantastic minds; a
      fantastic mistress.

   4. Resembling fantasies in irregularity, caprice, or
      eccentricity; irregular; oddly shaped; grotesque.

            There at the foot of yonder nodding beech, That
            wreathes its old fantastic roots so high. --T. Gray.

   Syn: Fanciful; imaginative; ideal; visionary; capricious;
        chimerical; whimsical; queer. See {Fanciful}.

Fantastic \Fan*tas"tic\, n.
   A person given to fantastic dress, manners, etc.; an
   eccentric person; a fop. --Milton.

         Our fantastics, who, having a fine watch, take all
         ocasions to drow it out to be seen.      --Fuller.

Source : WordNet®

fantastic
     adj 1: ludicrously odd; "Hamlet's assumed antic disposition";
            "fantastic Halloween costumes"; "a grotesque
            reflection in the mirror" [syn: {antic}, {fantastical},
             {grotesque}]
     2: extraordinarily good; used especially as intensifiers; "a
        fantastic trip to the Orient"; "the film was fantastic!";
        "a howling success"; "a marvelous collection of rare
        books"; "had a rattling conversation about politics"; "a
        tremendous achievement" [syn: {howling(a)}, {marvelous}, {marvellous},
         {rattling(a)}, {terrific}, {tremendous}, {wonderful}, {wondrous}]
     3: extravagantly fanciful and unrealistic; foolish; "a
        fantastic idea of his own importance"
     4: existing in fancy only; "fantastic figures with bulbous
        heads the circumference of a bushel"- Nathaniel Hawthorne
        [syn: {fantastical}]
     5: exceedingly or unbelievably great; "the bomb did fantastic
        damage"; "Samson is supposed to have had fantastic
        strength"; "phenomenal feats of memory" [syn: {phenomenal}]