Use the adjective chimerical to describe something that is wildly fanciful or imaginative — like the chimerical illustrations of unicorns in a children's book.
A chimera was a fire-breathing monster from Greek mythology made from three different animals: a lion at its head, a goat in the middle, and a serpent at the end. The first surviving mention of the beast is in Homer's The Iliad. From this fantastical creature, English created the adjective chimerical to describe wild figments of the imagination.
