Imaginary (adjective)

Existing only in the imagination; not real or actual.

Origin:

Late middle english: from latin imaginarius, from imago, imagin- 'image', influenced by medieval latin imaginarius 'belonging to imagination'.

Examples:

1. An imaginary friend is a companion that only exists in one's mind.
2. The dragon in the story was purely imaginary.
3. The town he built in his mind was an imaginary one.
4. She had an imaginary horse that she would often ride.
5. The pirate's treasure was just an imaginary prize that he claimed to have found.