Use 'fanciful' to describe ideas or stories that come from imagination instead of real life. His fanciful plan to travel to Mars ignored the limits of current technology.
Pro Tip 2/3
Unlikely Scenarios
'Fanciful' can suggest an idea is imaginative but unlikely to happen, often because it's too idealistic. Her proposal was dismissed as a fanciful notion by the committee.
Pro Tip 3/3
Creative but Unserious
'Fanciful' often hints that something is creative but not serious or practical. The author's fanciful characters captivated children but puzzled adults.