outrider n.

in Old English a common prefix with nouns, adjectives, adverbs, and verbs, "out, outward, outer; forth, away," from out (adv.). The use was even more common in Middle English, and also with the senses "outer, outside, on the outside, from without, external, externally; apart; greatly, extremely; completely, thoroughly, to completion." Other senses of out that extended into the use as a prefix include "beyond the surface or limits; to the utmost degree; to an explicit resolution."

In composition out has either its ordinary adverbial sense, as in outcast, outcome, outlook, etc., or a prepositional force, as in outdoors, or forms transitive verbs denoting a going beyond or surpassing of the object of the verb, in doing the act expressed by the word to which it is prefixed, as in outrun, outshine, outvenom, etc. In the last use especially out may be used with almost any noun or verb. [Century Dictionary]

late Old English ridere "one who rides, trooper, knight, mounted warrior," agent noun from ride (v.). Compare Middle Dutch rider, Dutch rijder, Old High German ritari, German Reiter, Old Norse riðeri; "It is uncertain how far the forms were independently developed in these languages" [OED]. As "one who is carried along on or in" (a chariot, cart, etc.), from c. 1200. Meaning "clause tacked on to a document after first draft" is from 1660s.