Chimerical (adjective)

Highly unrealistic and unlikely to be true or to happen; fanciful, visionary; existing only in the imagination.

Origin:

From late latin chimaera, from greek khimaira (she-goat), a mythical fire-breathing creature, from khimar (she-goat).

Examples:

1. His plan for a perpetual motion machine was considered chimerical.
2. The idea of a utopia is often considered chimerical.
3. It is chimerical to think that this product will sell itself.
4. He had the chimerical dream of becoming a millionaire.
5. The idea of creating a machine that can predict the future is chimerical.