Prose
The word "prose" first appears in English in the 14th century. It is derived from the Old French "prose", which in turn originates in the Latin expression "prosa oratio" (literally, straightforward or direct speech).
Republic
The term originates as the Latin translation of Greek word "politeia". Cicero, among other Latin writers, translated "politeia" as "res publica" and it was in turn translated by Renaissance scholars as "republic" (or similar terms in various western European languages).