'posteromedial' originates from Latin and Modern English combining forms, specifically from Latin 'posterus' (via the combining form 'postero-') and Latin 'medialis', where 'postero-' meant 'behind' and 'medial' meant 'middle or toward the midline'.

'posteromedial' formed by combining the classical/post-classical Latin elements 'postero-' (from 'posterus') and 'medial' (from 'medialis') into a compound descriptive adjective in modern anatomical English; it was built in the same way as other directional anatomical terms (e.g., 'anterolateral').

Initially the components meant 'behind' and 'middle/central' in Latin, and over time the compounded form has come to mean specifically 'both posterior and medial' in modern anatomical usage.