chimerical

Etymology

From chimera, from Latin chimaera, from Ancient Greek χίμαιρα (khímaira, “she-goat”). This term entered English in or around 1638.

adj

1. Of or pertaining to a chimera.
2. Being a figment of the imagination; fantastic (in the archaic sense).
   a chimerical goal
   Yes; I have a turn both for observation and for deduction. The theories which I have expressed there, and which appear to you to be so chimerical, are really extremely practical—so practical that I depend upon them for my bread and cheese. 1887, Arthur Conan Doyle, A Study in Scarlet
   With his head bent, and his big feet spread apart, he began explaining his reasons for thinking the abbé’s plan chimerical. 1869, Leon Tolstoy, War and Peace (Translated by Louise and Aylmer Maude)
3. Inherently fantastic; wildly fanciful.
4. (genetics) Resulting from the expression of two or more genes that originally coded for separate proteins.
5. (vision, of a perceived color) Impossible to physically produce due to having an impossibly-high saturation or luminosity, but viewable by overlaying an afterimage and a suitably-colored physical image.