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).
Toast (honor)
The word is, as mentioned above, of Latin origin and it comes from the verb "prodesse" (= "to benefit sth/sb", "to be beneficial"). Consequently, "prosit" is the conjugated form (3rd person Singular, Present Subjunctive, Active) and therefore an optative: "To you/ to your health". Like the colloquial "prost", "prosit" was originally used by university students.