'anencephalia' originates from New Latin and ultimately from Greek, specifically from Greek elements 'an-' meaning 'without' and 'enképhalos' meaning 'brain' (via New Latin/medical usage 'anencephalia').

'anencephalia' developed in medical New Latin from the Greek compound 'an- + enképhalos' (ἀν- + ἐγκέφαλος) meaning 'without brain'; it entered medical terminology in the 19th century as a term for the congenital condition and retained the form 'anencephalia' in scientific contexts.

Initially it literally meant 'without a brain' and over time has been used specifically to denote the congenital malformation now described as anencephaly or cases thereof; the core sense (absence of major brain structures) has been preserved.