'anencephalic' originates from New Latin/medical formation based on Greek elements: the prefix 'an-' (from Greek ἀν-) meaning 'without' and 'enkephalos' (Greek ἐγκέφαλος) meaning 'brain'.

'anencephalic' is formed from New Latin 'anencephalus/anencephalia' (19th century medical Latin), which itself comes from Greek 'an-' + 'enkephalos'; the English adjective developed in medical usage to describe the condition and those affected.

Initially it described the literal absence of the brain ('without brain'); over time it became the standard medical term for the congenital condition (anencephaly) and for describing individuals affected by it.