'pro-' originates from Latin, specifically the word 'pro', where 'pro' meant 'for, before, forward, on behalf of'.

'pro-' entered English as a combining form from Latin, passing into Late Latin/New Latin and then into English usage in the Middle to Early Modern English period, where it became common in learned and technical vocabulary (and later as a clipped standalone 'pro').

Initially it meant 'for' or 'forward' in Latin; over time it has remained largely consistent as a prefix meaning 'for'/'forward' and has also given rise to the clipped noun 'pro' meaning 'professional' or 'advantage'.