'pro-Christian' originates from Latin and Greek/Latin elements, specifically the prefix 'pro' (Latin) and 'Christianus' (Late Latin from Greek), where 'pro-' meant 'for' and 'Christos' meant 'anointed'.

'Christian' changed from the Greek word 'Christianos' to Late Latin 'Christianus' and into Old/Middle English as 'Christian'; the modern compound 'pro-Christian' was formed in Modern English by combining the prefix 'pro-' with 'Christian'.

Initially, the elements meant 'for' (pro-) and 'follower of the Anointed (Christ)' (Christian); over time the compound came to specifically mean 'supportive of Christianity' in contemporary usage.