'pro-mask' originates from Latin and from Italian/French: the prefix 'pro-' comes from Latin 'pro' where 'pro' meant 'for', and 'mask' comes via Italian 'maschera' or French 'masque' (from Medieval Latin 'masca').

'pro-mask' changed from the modern English compounding of the prefix 'pro-' and the noun 'mask' (the English 'mask' coming from Middle English 'maske'/'masque', ultimately from Italian/French forms) and eventually became the modern English compound 'pro-mask'.

Initially, 'pro-' meant 'for/forward' and 'mask' originally referred to 'a disguise, covering, or sometimes a specter'; over time the compound came to mean specifically 'in favor of wearing face coverings' in public-health or political contexts.