'pygidial' originates from New Latin 'pygidium', specifically the Greek word 'pygídion', where 'pyge' meant 'rump' or 'hindpart'.

'pygidial' changed from Greek 'pygídion' to Latin 'pygidium' (New Latin) and then entered English as the adjective 'pygidial' through scientific/biological Latin usage.

Initially it referred to the concrete structure 'pygidium' (the tail shield or small rump), but over time it evolved into the adjectival sense 'relating to the pygidium' (pertaining to the posterior terminal segment).