'pro-gun' originates from Modern English, specifically formed from the prefix 'pro-' (from Latin 'pro', meaning 'for') and the noun 'gun' (from Middle English 'gonne').

'gun' changed from the Middle English word 'gonne' (and earlier influences possibly including a Norse personal name such as 'Gunnhildr') and became the modern English 'gun'. The prefix 'pro-' comes from Latin 'pro' and entered English compounds; the modern compound 'pro-gun' arose as a political label in recent centuries.

Initially the elements meant 'for' (pro-) and 'firearm' (gun); combined they straightforwardly meant 'for guns' and evolved into a political descriptor meaning 'supportive of gun rights'.