A chimera is an imaginary creature made up of parts from different animals. The original Chimera from Greek mythology had a lion's head, a goat's body growing out of its back, and a serpent for a tail. It breathed fire and terrorized the countryside until a hero named Bellerophon defeated it while riding the winged horse Pegasus.

Today, scientists use chimera to describe a real organism that contains cells from two different individuals or species. Researchers might create a chimera by combining cells from different animals to study diseases or test new medicines. Some plants are natural chimeras, with branches that have different genetic makeup from each other.

The word also describes any impossible or wildly unrealistic idea. If your friend announces a plan to build a roller coaster in their backyard, learn five languages by next month, and become a professional soccer player by summer, you might say they're chasing a chimera. It means their dream is fantastical and unlikely to become real, just like the mythical creature that couldn't actually exist.

When something is described as chimerical, it means it's fanciful or purely imaginary: appealing to think about but impossible to achieve.