Acephaly is a term used in medical science to describe the absence of a head in a newborn. As the term is specific to this condition, there are no synonyms for acephaly as such. However, you can use terms like "headless" or "lacking a skull" to describe the condition in more general terms. Another way to convey the idea of a headless fetus or newborn is to use the more medical-sounding term "anencephaly," which also describes a congenital defect where the neural tube fails to close during fetal development. While these terms describe specific medical conditions, it is important to use them sensitively and with thought for the families and individuals affected by these conditions.