'posteromarginal' originates from Modern Latin/Neo-Latin, specifically from the combining form 'postero-' derived from Latin 'posterus' and the adjective 'marginalis' from Latin 'margo', where 'post-'/ 'posterus' meant 'after' or 'behind' and 'margo' meant 'edge'.

'posteromarginal' formed in scientific/medical usage by joining the prefix 'postero-' (from Latin via Neo-Latin anatomical formation) with 'marginal' (from Latin 'marginalis'); it entered English as a technical anatomical adjective describing location at a posterior margin.

Initially it described simply 'at the back edge' in technical descriptions; over time it has remained specialized and continues to mean 'located at or pertaining to the posterior margin' in anatomy and morphology.