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).
Myth
The word "myth" comes from Ancient Greek "μῦθος" ["mȳthos"], meaning 'speech, narrative, fiction, myth, plot'. In Anglicised form, this Greek word began to be used in English (and was likewise adapted into other European languages) in the early nineteenth century, in a much narrower sense, as a scholarly term for 'a traditional story, typically involving supernatural beings or forces, which embodies and provides an explanation, aetiology, or justification for something such as the early history of a society, a religious belief or ritual, or a natural phenomenon'.