Cyclopia: A congenital abnormality (birth defect) in which there is only one eye. That eye is centrally placed in the area normally occupied by the root of the nose. There is a missing nose or a nose in the form of a proboscis (a tubular appendage) located above the eye.
Cyclopia and milder forms of the same developmental disorder result from holoprosencephaly which is a failure of the embryonic forebrain to subdivide properly. (The embryonic forebrain is normally responsible for inducing the development of the orbits.) Chromosome abnormalities (such as trisomy 13) and gene mutations can disrupt this process. So also can certain toxins, some of them found in wild plants.
The term "cyclopia" comes from the Cyclops, the one-eyed giants of Greek mythology, a mythical race of lawless giant shepherds who lived in Sicily. They had a single large round eye in the center of the forehead. The word "cyclops" itself comes from the Greek "kyklos" (circle) + "ops" (eye). Cyclopia is also called synophthalmia.