'antero-posteriorly' originates from combining forms used in modern medical English: the prefix 'antero-' (from Latin 'ante', meaning 'before, in front') and 'posterior' (from Latin 'posterior', comparative of 'post', meaning 'after, behind'), with the adverbial suffix '-ly'.

'antero-posterior' developed in Modern/Neo-Latin and medical usage as a compound of 'anterior' + 'posterior' (both from Latin roots); the adverb 'antero-posteriorly' is the adverbial formation of that compound and entered English via scientific/medical literature in recent centuries.

Initially the components referred simply to 'before' and 'after' (front and back); over time the compounded form came to denote specifically the anatomical or directional axis 'front-to-back', a meaning retained in the modern adverb 'antero-posteriorly'.