'pro-republicanism' originates from 'English', specifically the word 'pro-' + 'republicanism', where 'pro-' meant 'in favor of' and 'republicanism' meant 'support for a republic'.

'republicanism' derives from 'republic', ultimately from Latin 'res publica' (literally 'public thing'); the modern English 'republicanism' developed via Old French and later English usage, and 'pro-' as a prefix (from Latin 'pro') was added in modern English to indicate support.

Initially, the elements meant 'in favor of' ('pro-') and 'the public/commonwealth' ('res publica'); over time these combined to express the modern sense of 'support for a republican form of government', a meaning that has largely remained consistent.