Figment (noun)

1. An invented or imagined thing.
2. A product of the imagination.

Origin:

Late middle english: from old french figment, from latin figmentum, from fingere "to shape, form, feign".

Examples:

1. The story was a figment of his imagination.
2. The evidence proved that the witness's testimony was a figment.
3. The creature in the movie was a figment of special effects.
4. The idea of a flying car is still a figment of science fiction.
5. The figment of his mind made him believe that he saw a ghost.