What is the term for an infant born without a brain?

The term "anacephalic" specifically refers to an infant born with a significant absence of brain tissue, particularly the absence of a major portion of the brain and skull. This condition, known as anencephaly, occurs during fetal development and results in the lack of a forebrain and the top part of the skull. Infants with this condition are typically not viable outside of the womb, as they lack the critical brain structures necessary for life.

The other terms do not accurately describe the condition of an infant born without a brain. "Cerebral" generally pertains to the brain itself but does not indicate any absence. "Hypodeveloped" implies underdevelopment but doesn't specifically denote the complete lack of a brain. "Impaired" is a broad term that can refer to various types of dysfunction or deficiency but does not specifically define a condition related to the absence of brain tissue. Therefore, "anacephalic" is the precise term for the condition described in the question.