anencephaly

The remote source is ancient Greek. Greek had the prefix an-, meaning "without," and enkephalos, meaning "brain." In classical Athens by the 5th century BCE, enkephalos named the organ inside the skull. The negative prefix could then turn presence into absence with blunt precision.

The medical path is modern, not ancient. In Paris and other European medical centers of the early 19th century, physicians built learned compounds from Greek pieces to classify congenital conditions. French anencéphalie is recorded in that period, and New Latin anencephalia circulated in medical writing soon after. English anencephaly followed in the mid 19th century as the standard noun.

The word is exact because its parts are exact. An- removes, enkephalos supplies the missing organ, and the ending -y in English makes the condition name fit medical vocabulary. The coinage belongs to the age when pathology, obstetrics, and teratology were building stable labels. It was formed to be clinical, not figurative.

Modern English keeps the term in medicine and public health. It refers to a severe congenital neural tube defect in which major parts of the brain and skull do not develop. The form has stayed close to its learned ancestors, even as pronunciation shifted into English patterns. Its history is short in English but old in its Greek bones.