prefix usually meaning "away, opposite, completely," from Old English for-, indicating loss or destruction, but in other cases completion, and used as well with intensive or pejorative force, from Proto-Germanic *fur "before, in" (source also of Old Norse for-, Swedish för-, Dutch ver-, Old High German fir-, German ver-); from PIE *pr-, from root *per- (1) "forward," hence "in front of, before, toward, near, against."
In verbs the prefix denotes (a) intensive or completive action or process, or (b) action that miscarries, turns out for the worse, results in failure, or produces adverse or opposite results. In many verbs the prefix exhibits both meanings, and the verbs frequently have secondary and figurative meanings or are synonymous with the simplex. [Middle English Compendium]
Probably originally in Germanic with a sense of "forward, forth," but it spun out complex sense developments in the historical languages. Disused as a word-forming element in Modern English. Ultimately from the same root as fore (adv.). From its use in participles it came to be an intensive prefix of adjectives in Middle English (for example Chaucer's forblak "exceedingly black"), but all these now seem to be obsolete.
From late Old English as "in favor of." For and fore differentiated gradually in Middle English. For alone as a conjunction, "because, since, for the reason that; in order that" is from late Old English, probably a shortening of common Old English phrases such as for þon þy "therefore," literally "for the (reason) that."
Meaning "place of standing, position" is from early 14c.; figurative sense is from 1590s. Meaning "raised platform for a hunter or sportsman" is attested from c. 1400. Meaning "raised platform for spectators at an open-air event" is from 1610s; meaning "piece of furniture on which something is to be set" is from 1690s. Sense of "stall or booth" is first recorded c. 1500. Military meaning "complete set" (of arms, colors, etc.) is from 1721, often a collective singular. Sense of "standing growth" (usually of of trees) is 1868, American English. Theatrical sense of "each stop made on a performance tour" is from 1896. The word formerly also was slang for "an erection" (1867).
Old English standan "occupy a place; stand firm; congeal; stay, continue, abide; be valid, be, exist, take place; oppose, resist attack; stand up, be on one's feet; consist, amount to" (class VI strong verb; past tense stod, past participle standen), from Proto-Germanic *standanan (source also of Old Norse standa, Old Saxon and Gothic standan, Old High German stantan, parallel with simpler forms, such as Swedish stå, Dutch staan, German stehen [see discussion in OED]), from *stathula, from PIE root *sta- "to stand, make or be firm."
Sense of "to exist, be present" is attested from c. 1300. Meaning "encounter without flinching" is from 1590s; weaker sense of "put up with" is from 1620s. Meaning "to submit" (to chances, etc.) is from c. 1700. Meaning "to pay for as a treat" is from 1821. Meaning "become a candidate for office" is from 1550s. Nautical sense of "hold a course at sea" is from 1620s. Meaning "to be so high when standing" is from 1831.
Stand back "keep (one's) distance" is from c. 1400. Phrase stand pat is from poker (1882), earlier simply stand (1824 in other card games). To stand down is from 1680s, originally of witnesses in court; in the military sense of "come off duty" it is first recorded 1916. To let (something) stand is from c. 1200. To stand for is c. 1300 as "count for;" early 14c. as "be considered in lieu of;" late 14c. as "represent by way of sign;" sense of "tolerate" first recorded 1620s. Phrase stands to reason (1620) is from earlier stands (is constant) with reason.