replay v.

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]

Middle English pleien, from Old English plegan, plegian "move lightly and quickly, occupy or busy oneself, amuse oneself; engage in active exercise; frolic; engage in children's play; make sport of, mock; perform music," from Proto-West Germanic *plegōjanan "occupy oneself about" (source also of Old Saxon plegan "vouch for, take charge of," Old Frisian plega "tend to," Middle Dutch pleyen "to rejoice, be glad," German pflegen "take care of, cultivate"), which is apparently connected to the root of plight (v.), but the ultimate etymology is uncertain and the phonetic development is difficult to explain.

Meaning "to take part in" a martial or athletic game is from c. 1200. It has been opposed to work (v.) since late 14c. Meaning "perform or act on the stage" (transitive) is by late 14c., as are the senses of "take the role of" and "make a pretense of, make believe" and "act thoughtlessly or wantonly." Sense of "put forward, move, throw, lay on the table, etc." in the course of a game or contest is by 1560s of chess pieces, 1670s of playing cards. Sense of "operate or cause to operate with continuous or repeated action" is from 1590s. Meaning "to cause (a recording) to reproduce what is on it" is by 1903, probably from the "make music" sense. Related: Played; playing.

Many expressions are from the stage, sports and games, or music, and it is not always easy to say which is from which. To play up "emphasize" is from 1909 (perhaps originally "play music more vigorously"); to play down "minimize" is from 1930; to play along "pretend to agree or cooperate" is from 1929. To play fair "be nice" is from mid-15c. To play house as a children's activity is from 1958.

To play for keeps is from 1861, originally of marbles or other children's games with tokens. To play (something) safe is from 1911; to play favorites is attested from 1902.  To play second fiddle in the figurative sense is from 1809 ("Gil Blas"). To play into the hands (of someone) "act in such a way as to give the advantage to one's opponent or a third party" is from 1705. For play the _______ card see card (n.1). For play the field see field (n.). To play with oneself "masturbate" is from 1896 (to play with "have sexual intercourse with" is from mid-13c.). Playing-card "one of a pack of cards used for playing games" is from 1540s.