'pes' originates from Latin, specifically the word 'pes', where 'pes' meant 'foot' (from Proto-Indo-European root *ped- meaning 'foot').

'pes' entered English as a technical term via Medieval/Scientific Latin and has been retained in anatomy, zoology, and paleontology as a specialized borrowing from Latin.

Initially, it meant 'foot' in Latin, and over time it evolved into its current use as a technical term in English with essentially the same basic meaning of 'animal foot'.