'pro-clerical' originates from the Latin prefix 'pro-' meaning 'for' combined with 'clerical,' which ultimately comes from Late Latin 'clericus' meaning 'clergyman' (via Old French 'clerc').

'clerical' changed from Late Latin 'clericus' to Old French 'clerc' and Middle English 'clerc/cleric', becoming the English adjective 'clerical'; the prefix 'pro-' (from Latin 'pro-') was attached in modern English to form 'pro-clerical'.

Initially, the root 'clericus' meant 'clergyman' and 'clerical' meant 'relating to the clergy'; with the addition of 'pro-' the compound came to mean 'in favor of the clergy or church influence,' which is how it is used today.