word-forming element meaning "back, back from, back to the original place;" also "again, anew, once more," also conveying the notion of "undoing" or "backward," etc. (see sense evolution below), c. 1200, from Old French re- and directly from Latin re- an inseparable prefix meaning "again; back; anew, against."

Watkins (2000) describes this as a "Latin combining form conceivably from Indo-European *wret-, metathetical variant of *wert- "to turn." De Vaan says the "only acceptable etymology" for it is a 2004 explanation which reconstructs a root in PIE *ure "back."

In earliest Latin the prefix became red- before vowels and h-, a form preserved in redact, redeem, redolent, redundant, redintegrate, and, in disguise, render (v.). In some English words from French and Italian re- appears as ra- and the  following consonant is often doubled (see rally (v.1)).

The many meanings in the notion of "back" give re- its broad sense-range: "a turning back; opposition; restoration to a former state; "transition to an opposite state." From the extended senses in "again," re- becomes "repetition of an action," and in this sense it is extremely common as a formative element in English, applicable to any verb. OED writes that it is "impossible to attempt a complete record of all the forms resulting from its use," and adds that "The number of these is practically infinite ...."   

Often merely intensive, and in many of the older borrowings from French and Latin the precise sense of re- is forgotten, lost in secondary senses, or weakened beyond recognition, so that it has no apparent semantic content (receive, recommend, recover, reduce, recreate, refer, religion, remain, request, require). There seem to have been more such words in Middle English than after, e.g. recomfort (v.) "to comfort, console; encourage;" recourse (n.) "a process, way, course." Recover in Middle English also could mean "obtain, win" (happiness, a kingdom, etc.) with no notion of getting something back, also "gain the upper hand, overcome; arrive at;" also consider the legal sense of recovery as "obtain (property) by judgment or legal proceedings." 

And, due to sound changes and accent shifts, re- sometimes entirely loses its identity as a prefix (rebel, relic, remnant, restive, rest (n.2) "remainder," rally (v.1) "bring together"). In a few words it is reduced to r-, as in ransom (a doublet of redemption), rampart, etc.

It was used from Middle English in forming words from Germanic as well as Latin elements (rebuild, refill, reset, rewrite), and was used so even in Old French (regret, regard, reward, etc.).

Prefixed to a word beginning with e, re- is separated by a hyphen, as re-establish, re-estate, re-edify, etc. ; or else the second e has a dieresis over it: as, reëstablish, reëmbark, etc. The hyphen is also sometimes used to bring out emphatically the sense of repetition or iteration : as, sung and re-sung. The dieresis is not used over other vowels than e when re is prefixed : thus, reinforce, reunite, reabolish. [Century Dictionary, 1895]

*stā-, Proto-Indo-European root meaning "to stand, set down, make or be firm," with derivatives meaning "place or thing that is standing."

It forms all or part of: Afghanistan; Anastasia; apostasy; apostate; armistice; arrest; assist; astatic; astatine; Baluchistan; bedstead; circumstance; consist; constable; constant; constitute; contrast; cost; desist; destination; destine; destitute; diastase; distance; distant; ecstasy; epistasis; epistemology; establish; estaminet; estate; etagere; existence; extant; Hindustan; histidine; histo-; histogram; histology; histone; hypostasis; insist; instant; instauration; institute; interstice; isostasy; isostatic; Kazakhstan; metastasis; obstacle; obstetric; obstinate; oust; Pakistan; peristyle; persist; post (n.1) "timber set upright;" press (v.2) "force into service;" presto; prostate; prostitute; resist; rest (v.2) "to be left, remain;" restitution; restive; restore; shtetl; solstice; stable (adj.) "secure against falling;" stable (n.) "building for domestic animals;" stage; stalag; stalwart; stamen; -stan; stance; stanchion; stand; standard; stanza; stapes; starboard; stare decisis; stasis; -stat; stat; state (n.1) "circumstances, conditions;" stater; static; station; statistics; stator; statue; stature; status; statute; staunch; (adj.) "strong, substantial;" stay (v.1) "come to a halt, remain in place;" stay (n.2) "strong rope which supports a ship's mast;" stead; steed; steer (n.) "male beef cattle;" steer (v.) "guide the course of a vehicle;" stem (n.) "trunk of a plant;" stern (n.) "hind part of a ship;" stet; stoa; stoic; stool; store; stound; stow; stud (n.1) "nailhead, knob;" stud (n.2) "horse kept for breeding;" stylite; subsist; substance; substitute; substitution; superstition; system; Taurus; understand.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit tisthati "stands;" Avestan histaiti "to stand;" Persian -stan "country," literally "where one stands;" Greek histēmi "put, place, cause to stand; weigh," stasis "a standing still," statos "placed," stylos "pillar;" Latin sistere "stand still, stop, make stand, place, produce in court," status "manner, position, condition, attitude," stare "to stand," statio "station, post;" Lithuanian stojuos "I place myself," statau "I place;" Old Church Slavonic staja "place myself," stanu "position;" Gothic standan, Old English standan "to stand," stede "place;" Old Norse steði "anvil;" Old Irish sessam "the act of standing."

"an eating-house, establishment where meals may be bought and eaten," 1821, from French restaurant "a restaurant," originally "food that restores," noun use of present participle of restaurer "to restore or refresh," from Old French restorer (see restore).

In 1765 a man by the name of Boulanger, also known as "Champ d'Oiseaux" or "Chantoiseau," opened a shop near the Louvre (on either the rue des Poulies or the rue Bailleul, depending on which authority one chooses to believe). There he sold what he called restaurants or bouillons restaurants—that is, meat-based consommés intended to "restore" a person's strength. Ever since the Middle Ages the word restaurant had been used to describe any of a variety of rich bouillons made with chicken, beef, roots of one sort or another, onions, herbs, and, according to some recipes, spices, crystallized sugar, toasted bread, barley, butter, and even exotic ingredients such as dried rose petals, Damascus grapes, and amber. In order to entice customers into his shop, Boulanger had inscribed on his window a line from the Gospels: "Venite ad me omnes qui stomacho laboratis et ego vos restaurabo." He was not content simply to serve bouillon, however. He also served leg of lamb in white sauce, thereby infringing the monopoly of the caterers' guild. The guild filed suit, which to everyone's astonishment ended in a judgment in favor of Boulanger. [Jean-Robert Pitte, "The Rise of the Restaurant," in "Food: A Culinary History from Antiquity to the Present," English editor Albert Sonnenfeld, transl. Clarissa Botsford, 1999, Columbia University Press]

Italian spelling ristorante attested in English by 1925. Middle English had similar words in legal language, such as restaurance "restitution." The railroad restaurant car (1872) was one adapted to afford meals to passengers while travelling. 

late 14c., restoracioun, "a means of healing or restoring health, a cure; renewing of something lost," from Old French restoration (Modern French restauration) and directly from Late Latin restorationem (nominative restoratio) "a restoration, renewal," noun of action from past-participle stem of Latin restaurare (see restore).

Also used in Middle English were restorement (14c.), restoring (mid-14c.). From mid-15c. as "the repairing of a damaged or deteriorated building;" from c. 1500 as "a restoring to a former state."

The Restoration (1718) refers to the re-establishment of the monarchy under Charles II in 1660 (and by extension his whole reign); as an adjective in reference to the English theater of this period, by 1898. In French history, it refers to the (briefly interrupted) reinstatement of the Bourbons in 1814.

"capable of restoring health or strength," late 14c., restoratif, from Old French restoratif, restauratif, from restorer (see restore) or from Medieval Latin restaurativus.

early 15c., restorour, in medicine (Chauliac), "one who resets a dislocation," from Old French restoreor, agent noun from restorer (see restore (v.)).

mid-13c., "to supply or stock," from Old French estorer "erect, construct, build; restore, repair; furnish, equip, provision," from Latin instaurare "to set up, establish; renew, restore," in Medieval Latin also "to provide, store," from in- "in" (from PIE root *en "in") + -staurare, from PIE *stau-ro-, suffixed extended form of root *sta- "to stand, make or be firm" (compare restore). The meaning "to keep in store for future use" (1550s) probably is a back-formation from store (n.). Related: Stored; storing.