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]
stretch v.
Old English streccan (transitive and intransitive) "to stretch, spread out, prostrate; reach, extend" (past tense strehte, past participle streht), from Proto-Germanic *strakjanan (source also of Danish strække, Swedish sträcka, Old Frisian strekka, Old High German strecchan, Middle Low German, Middle Dutch, Old High German, German strecken "to stretch, draw out"), perhaps a variant of the root of stark, or else from PIE root *strenk- "tight, narrow; pull tight, twist" (see string (n.)).
Meaning "to extend (the limbs or wings)" is from c. 1200; that of "to lay out for burial" is from early 13c. To stretch (one's) legs "take a walk" is from c. 1600. Meaning "to lengthen by force" first recorded late 14c.; figurative sense of "to enlarge beyond proper limits, exaggerate," is from 1550s. Stretch limo first attested 1973. Stretch marks is attested from 1960. Related: Stretched; stretching.