remarry 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]

c. 1300, marien, of parents or superiors, "to give (offspring) in marriage," also intransitive, "to enter into the conjugal state, take a husband or wife," from Old French marier "to get married; to marry off, give in marriage; to bring together in marriage," from Latin marītāre "to wed, marry, give in marriage" (source of Italian maritare, Spanish and Portuguese maridar), from marītus (n.) "married man, husband," which is of uncertain origin.

Perhaps ultimately "provided with a *mari," a young woman, from PIE *mari-, *mori- "young wife, young woman" (source also of Welsh morwyn "girl, maiden," Middle Welsh merch "daughter"), akin to *meryo- "young man" (source of Sanskrit marya- "young man, suitor").

By early 14c. as "to take (someone) in marriage, take for a husband or wife;" by late 14c. as "become husband and wife according to law or custom; get married (to one another)." Transitive sense, of a priest, etc., who performs the rite of marriage, "to unite in wedlock or matrimony," by 1520s.

Figurative meaning "unite intimately or by some close bond of connection" is from early 15c. Related: Married; marrying. Phrase the marrying kind, describing one inclined toward marriage and almost always used with a negative, is attested by 1824, probably short for marrying kind of men, which is from a popular 1756 essay by Chesterfield.

In some Indo-European languages there were distinct "marry" verbs for men and women, though some of these have become generalized. Compare Latin ducere uxorem (of men), literally "to lead a wife;" nubere (of women), perhaps originally "to veil" [Buck]. Also compare Old Norse kvangask (of men) from kvan "wife" (see quean), so, "take a wife;" giptask (of women), from gipta, a specialized use of "to give" (see gift (n.)), so, "to be given."