1. ludicrously odd

- fantastic Halloween costumes

Similar word(s): strange, unusual, antic, fantastical, grotesque

2. extraordinarily good or great; used especially as intensifiers

- a fantastic trip to the Orient

- the film was fantastic!

Similar word(s): extraordinary, grand, howling, marvellous, marvelous, rattling, terrific, tremendous, wonderful, wondrous, raging

3. fanciful and unrealistic; not believable.

- a fantastic idea of his own importance

Similar word(s): unrealistic, wild

4. existing in fancy only

- fantastic figures with bulbous heads the circumference of a bushel

Similar word(s): unreal, fantastical

5. extravagantly fanciful in design, construction, appearance

- Gaudi's fantastic architecture

Similar word(s): fancy

Sentences with fantastic as an adjective:

- He told fantastic stories of dragons and goblins.

- His fantastic post-college plans had all collapsed within a year of graduation.

- She had a fantastic view of her own importance that none of her colleagues shared.

- The events were so fantastic that only the tabloids were willing to print them.

- She entered the lab and stood gaping for a good ten minutes at the fantastic machinery at work all around her.

- "I had a simply fantastic vacation, and I can't wait to tell you all about it!"