'posteromedially' originates from modern medical English, formed from the combining form 'postero-' (from Latin 'posterus'/'posterior' meaning 'behind' or 'coming after') and 'medial' (from Latin 'medialis', from 'medius' meaning 'middle'), plus the adverbial suffix '-ly'.

'posteromedial' arose in Neo-Latin/modern anatomical terminology by combining 'postero-' (a combining form derived from Latin through Late Latin/Medieval Latin) with 'medial'; the adverb 'posteromedially' was then created by adding the English adverbial suffix '-ly'.

The component roots originally meant 'behind' and 'middle'; over time the combined term came to be used specifically in anatomy to denote direction or position 'toward the back and toward the midline'.