WordWeb Online

1. Extraordinarily good or great; used especially as an intensifier
   "a fantastic trip to the Orient"; "the film was fantastic!";
   - grand, howling, marvelous [US], marvellous [Brit, Cdn], rattling, terrific, tremendous, wonderful, wondrous, magnificent, heavenly
    
2. Ludicrously odd
   "fantastic Halloween costumes";
   - antic [archaic], fantastical, grotesque
    
3. Fanciful and unrealistic; foolish
   "a fantastic idea of his own importance";
   - wild
    
4. Existing in fancy only
   "fantastic figures with bulbous heads the circumference of a bushel";
   - fantastical
    
5. Extravagantly fanciful in design, construction, appearance
   "Gaudi's fantastic architecture"

See also: extraordinary, fancy, strange, unreal, unrealistic, unusual

Encyclopedia: Fantastic