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).
Poetic diction
In Iceland, Snorri Sturluson wrote the "Prose Edda", a.k.a. the "Younger Edda" around 1200 A.D., partially to explain the older "Edda" and poetic diction. Half of the "Prose Edda", the Skáldskaparmál ("language of poetry creation" or "creative language of poets"), is a manual of traditional Icelandic poetic diction, containing a list of kennings. The list is systematized so as to function as a practical thesaurus for the use of poets wishing to write in the genuine old manner, and structured as an FAQ. Snorri gives traditional examples and also opens the way for creating correct new kennings: