The word "therewith" is a compound adverb formed in Middle English by directly combining the Old English words "there" and "with." Its formation follows a common Germanic pattern of creating compound adverbs to express relational concepts. Literally meaning "with that (thing just mentioned)," it originally denoted close association or accompaniment in a physical or temporal sense. Over time, its meaning expanded from the concrete ("along with that object") to more abstract and legalistic senses, such as indicating a consequent action or an additional item, which are its primary uses in modern formal and literary English.

Structure: there + with - there: From Old English þǣr, þār (in or at that place). A demonstrative adverb of place. - with: From Old English wiþ (against, opposite, toward, by, near). A preposition indicating association or accompaniment.