'pro-papal' originates from Latin: the prefix 'pro-' (Latin 'pro') meaning 'for' and 'papal' from Latin 'pāpalis' (from 'pāpa') where 'pāpa' meant 'pope' or 'father'.

'papal' came into English via Latin 'pāpalis' (and Old French 'papal') and Middle English 'papal'; the prefix 'pro-' (Latin 'pro', 'for') was attached in Modern English to form the compound 'pro-papal'.

Initially the elements literally signified 'for the pope/pope-related'; over time the compound has come to mean 'supporting the pope or the papacy' in political and religious contexts.