'posteroanteriorly' originates from Latin combining forms: the prefix 'postero-' (from Latin 'posterus'/'poster-' meaning 'behind, coming after') combined with 'anterior' (from Latin 'ante-' meaning 'before'), plus the English adverbial suffix '-ly'.

'posterior' and 'anterior' were Latin adjectives; in medical and anatomical English the combining form 'postero-' was attached to 'anterior' to form 'posteroanterior' (used to describe direction or relation), and English added the adverbial suffix '-ly' to produce 'posteroanteriorly'.

Initially the components described relative position ('behind' and 'before'); over time the combined term evolved into a specific directional adverb meaning 'from the back toward the front'.