'postero-pygidial' originates from Latin and Ancient Greek, specifically the Latin 'posterus' (or the combining form 'postero-') where 'poster-' meant 'behind' and the Greek 'pygidion' where 'pygid-' meant 'rump' or 'rear'.

'postero-pygidial' is a modern compound formed in scientific/technical (Neo-Latin/English) usage by combining the Latin-derived prefix 'postero-' with the adjective 'pygidial' (from Neo-Latin 'pygidium' < Greek 'pygidion'), producing a descriptive adjective used in entomology and arthropod morphology.

Initially the roots referred simply to 'behind' and 'rump'; in modern scientific usage they combine to mean 'pertaining to the rear portion of the pygidium,' a specialized anatomical descriptor with little semantic drift.