early 14c., reconisaunce, in law, "a bond acknowledging some obligation binding one over to do some particular act," from Old French reconissance "acknowledgment, recognition" (12c., Modern French reconnaissance), from reconoiss-, present-participle stem of reconoistre (see recognize).

By c. 1400 as "acknowledgment of subjection or allegiance" (to God or a temporal power). The general sense of "act of recognizing, acknowledgement of a person or thing" is from 15c. To be discharged or released (up)on (one's) own recognizance (1851) as a phrase for "be released without bail on condition of good behavior" in the jargon of police blotters and district courts, is based on the written promise that you sign to get it, to appear in court as required. Related: Recognizant.

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]

mid-14c., conisance, "device or mark by which something or someone is known," from Anglo-French conysance "recognition," later, "knowledge," from Old French conoissance "acquaintance, recognition; knowledge, wisdom" (Modern French connaissance), from past participle of conoistre "to know," from Latin cognoscere "to get to know, recognize," from assimilated form of com "together" (see co-) + gnoscere "to know" (from PIE root *gno- "to know").

Meaning "knowledge by observation or notice, understanding, information" is from c. 1400. In law, "the exercise of jurisdiction, the right to try a case" (mid-15c.). Meaning "acknowledgment, admission" is from 1560s. The -g- was restored in English spelling 15c. and has gradually affected the pronunciation, which was always "con-." The old pronunciation lingered longest in legal use.

*gnō-, Proto-Indo-European root meaning "to know."

It forms all or part of: acknowledge; acquaint; agnostic; anagnorisis; astrognosy; can (v.1) "have power to, be able;" cognition; cognizance; con (n.2) "study;" connoisseur; could; couth; cunning; diagnosis; ennoble; gnome; (n.2) "short, pithy statement of general truth;" gnomic; gnomon; gnosis; gnostic; Gnostic; ignoble; ignorant; ignore; incognito; ken (n.1) "cognizance, intellectual view;" kenning; kith; know; knowledge; narrate; narration; nobility; noble; notice; notify; notion; notorious; physiognomy; prognosis; quaint; recognize; reconnaissance; reconnoiter; uncouth; Zend.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit jna- "know;" Avestan zainti- "knowledge," Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati "recognizes," Russian znat "to know;" Latin gnoscere "get to know," nobilis "known, famous, noble;" Greek gignōskein "to know," gnōtos "known," gnōsis "knowledge, inquiry;" Old Irish gnath "known;" German kennen "to know," Gothic kannjan "to make known."

chiefly British English spelling of recognize; for spelling, see -ize. Related: Recognised; recognising; recognisance; recognisable.

mid-15c., recognicion, "knowledge (of an event or incident); understanding," from Old French recognition (15c.) and directly from Latin recognitionem (nominative recognitio) "a reviewing, investigation, examination," noun of action from past-participle stem of recognoscere "to acknowledge, know again; examine" (see recognize).

Sense of "acknowledgment of a service or kindness done" is from 1560s. Sense of "formal avowal of knowledge and approval" (as between governments or sovereigns) is from 1590s; especially acknowledgement of the independence of a country by a state formerly exercising sovereignty (1824). The meaning "a knowing again, consciousness that a given object is identical with an object previously recognized" is by 1798 (Wordsworth). The literary (especially stage) recognition scene "scene in which a principal character suddenly learns or realizes the true identity of another character" is by 1837 (in a translation from German).

"able to be recognized, capable of being known and acknowledged," 1751; see recognize (v.) + -able. Related: Recognizably; recognizability.

"act of recognizing," 1550s, from recognize + noun ending -ation.

also reconnoitre, 1707, "make a survey," specifically "to examine a tract or region for military or engineering purposes," from older French reconnoitre (Modern French reconnaître), from Old French reconoistre "to identify" (see recognize). Related: Reconnoitering.