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).
Mess
The root of "mess" is the Old French "mes", "portion of food" (cf. modern French "mets"), drawn from the Latin verb "mittere", meaning "to send" and "to put" (cf. modern French "mettre"), the original sense being "a course of a meal put on the table"; cfr. also the modern Italian "portata" with the same meaning, past participle of "portare", "to bring". This sense of "mess", which appeared in English in the 13th century, was often used for cooked or liquid dishes in particular, as in the "mess of pottage" (porridge or soup) or Eton mess.