The difference between Fantastic and Unrealistic

When used as adjectives, fantastic means existing in or constructed from fantasy, whereas unrealistic means not realistic.

Fantastic is also noun with the meaning: a fanciful or whimsical person.

check bellow for the other definitions of Fantastic and Unrealistic

Fantastic as an adjective:

Existing in or constructed from fantasy; of or relating to fantasy; fanciful.

Examples:

"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."
Fantastic as an adjective:

Not believable; implausible; seemingly only possible in fantasy.

Examples:

"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."
Fantastic as an adjective:

Resembling fantasies in irregularity, caprice, or eccentricity; irregular; grotesque.
Fantastic as an adjective:

Wonderful; marvelous; excellent; extraordinarily good or great (used especially as an intensifier).

Examples:

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