'pro-Constitution' is formed from the Latin prefix 'pro-' (originating from Latin, where 'pro' meant 'for' or 'in favor of') combined with 'Constitution' (originating from Latin 'constitutio'), where 'constitutio' comes from 'constituere' meaning 'to set up, establish'.

'Constitution' entered English via Old French/Medieval Latin forms (e.g. Medieval Latin 'constitutio' and Anglo-Norman/French 'constitution') and through Middle English became the modern English 'Constitution'; the modern compound 'pro-Constitution' is a contemporary formation using the prefix 'pro-' + 'Constitution'.

Initially 'constitutio' meant 'a setting up' or 'establishment' in Latin, but over time the meaning evolved into the modern sense of 'a system of fundamental principles or established precedents according to which a state is governed'—and 'pro-' added the sense 'in favor of', producing 'pro-Constitution' meaning 'in favor of the constitution'.