'pro-medievalist' is formed from the prefix 'pro-' (from Latin 'pro', meaning 'for' or 'in favor of') attached to 'medievalist' (a person concerned with or studying the Middle Ages).

'Medieval' ultimately comes from Medieval Latin 'medium aevum' meaning 'middle age'; that gave rise to French 'médiéval' and then English 'medieval'. The agentive suffix '-ist' produced 'medievalist' (a specialist or advocate), and the prefix 'pro-' was later attached to signal being 'for' or supportive, yielding 'pro-medievalist'.

Initially, 'medieval' described the historical period 'the middle ages'; over time 'medievalist' came to mean someone who studies or values that period, and adding 'pro-' specifically marked someone as supportive of medievalism or medievalist positions.