Anencephalous

Part of speech: adjective

Definitions

1. A medical term describing a severe birth defect where most of the brain and skull fail to develop during fetal growth
2. Characterized by the absence or severe underdevelopment of the brain and skull vault due to failed neural tube closure during gestation
3. A term used in medicine to refer to a condition where there is a significant lack of brain tissue and cranial structure due to developmental issues in the fetus

Etymology: "Anencephalous" is a case where the Greek building blocks are more transparent than the medicine they describe. The Greek adjective "anenképhalos" meant "brainless," formed from "an-," the familiar negative prefix meaning "not," and "enképhalos," which combined "en-" ("in") with "kephalē" ("head"), so the literal sense is something like "in the head," the organ that lay inside the skull. Greek physicians and writers used the word in its plain sense of lacking a brain, a description that carried no clinical precision and certainly no notion of a developmental disorder. The English term is a modern medical coinage built from those classical parts. Its specific meaning, a condition in which most of the brain and skull fail to form during fetal development, belongs to the age of modern anatomy and embryology rather than to ancient medicine. The ancient Greeks had no concept of this defect as a named pathology, so the word's technical sense is a later repurposing of an old descriptive adjective.