Which word refers to a grotesque product of the imagination?

The term that refers to a grotesque product of the imagination is "chimera." In classical mythology, a chimera is often depicted as a creature composed of parts from different animals, combining features in a fantastical and often bizarre way. In a broader sense, it can also represent an unrealistic dream or a fanciful idea that is illusory or fantastical in nature. This aligns perfectly with the definition of something grotesque and imaginative, highlighting the blend of the absurd and the creative.

The other options, while related to imagination in various ways, do not convey the same connotation of something unusual or monstrous. "Fantasy" refers more to an imaginative scenario or state, "illusion" pertains to a misleading perception of reality, and "fiction" denotes a narrative or story that is invented but does not necessarily imply grotesqueness. None capture the specific combination of imagination and grotesque quality like "chimera" does.