Online Etymology Dictionary

reckless (adj.): Old English receleas "careless, thoughtless, heedless," earlier reccileas, from *rece, recce "care, heed," from reccan "to care" (see reck (v.)) + -less. The same affixed form is in German ruchlos, Dutch roekeloos "wicked." Root verb reck (Old English reccan) is passing into obscurity.
recklessly (adv.): Old English recceleaslice; see reckless + -ly (2).
recklessness (n.): Old English recceleasnes "recklessness, carelessness, negligence;" see reckless + -ness.
reckon (v.): c. 1200, recenen, from Old English gerecenian "to explain, relate, recount," from Proto-Germanic *(ga)rekenojan (source also of Old Frisian rekenia, Middle Dutch and Dutch rekenen, Old High German rehhanon, German rechnen, Gothic rahnjan "to count, reckon"), from Proto-Germanic *rakina- "ready, straightforward," from PIE *reg- "to move in a straight line," with derivatives meaning "direct in a straight line, rule" (see regal).

Intransitive sense "make a computation" is from c. 1300. In I reckon, the sense is "hold an impression or opinion," and the expression, used parenthetically, dates from c. 1600 and formerly was in literary use (Richardson, etc.), but came to be associated with U.S. Southern dialect and was regarded as provincial or vulgar. Related: Reckoned; reckoning.
reckoner (n.): early 13c., agent noun from reckon. Especially "book of tables used in calculation," often known as a ready reckoner.
reckoning (n.): early 14c., "narrative, account," verbal noun from reckon (v.). Meaning "a settling of accounts" is from mid-14c.; that of "calculation" is from late 14c. Compare Dutch rekening "a bill, account, reckoning," Old High German rechenunga, German rechnung, Danish regning "a reckoning, computation." Day of reckoning attested from c. 1600.
reclaim (v.): early 14c., "call back a hawk to the glove," from Old French reclamer "to call upon, invoke; claim; seduce; to call back a hawk" (12c.) and directly from Latin reclamare "cry out against, contradict, protest, appeal," from re- "opposite, against" (see re-) + clamare "cry out" (see claim (v.)).

"Call back a hawk," hence "to make tame" (mid-15c.), "subdue, reduce to obedience, make amenable to control" (late 14c.). In many Middle English uses with no sense of return or reciprocation. Meaning "revoke" (a grant, gift, etc.) is from late 15c. That of "recall (someone) from an erring course to a proper state" is mid-15c. Sense of "get back by effort" might reflect influence of claim. Meaning "bring waste land into useful condition fit for cultivation" first attested 1764, probably on notion of "reduce to obedience." Related: Reclaimed; reclaiming.
reclamation (n.): late 15c., "a revoking" (of a grant, etc.), from Old French réclamacion and directly from Latin reclamationem (nominative reclamatio) "a cry of 'no,' a shout of disapproval," noun of action from past participle stem of reclamare "cry out against, protest" (see reclaim). From 1630s as "action of calling (someone) back" (from iniquity, etc.); meaning "action of claiming something taken awat" is from 1787. Of land from 1848.
recline (v.): early 15c., from Old French recliner "rest, lay; bend, lean over" (13c.) and directly from Latin reclinare "to bend back, to lean back; cause to lean," from re- "back, against" (see re-) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei "to lean" (see lean (v.)). Related: Reclined; reclining.
Recline is always as strong as lean, and generally stronger, indicating a more completely recumbent position, and approaching lie. [Century Dictionary]
recliner (n.): 1660s, agent noun from recline. From 1880 as a type of chair.
recluse (n.): c. 1200, "person shut up from the world for purposes of religious meditation," from Old French reclus (fem. recluse) "hermit, recluse," also "confinement, prison; convent, monastery," noun use of reclus (adj.) "shut up," from Late Latin reclusus, past participle of recludere "to shut up, enclose" (but in classical Latin "to throw open"), from Latin re-, intensive prefix, + claudere "to shut" (see close (v.)).
reclusive (adj.): 1590s, from recluse + -ive. Recluse alone formerly served also as an adjective in English (early 13c.).
recognise (v.): chiefly British English spelling of recognize; for spelling, see -ize. Related: Recognised; recognising; recognisance.
recognition (n.): mid-15c., "knowledge of an event or incident; understanding," from Middle 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 "formal avowal of knowledge and approval" is from 1590s; especially acknowledgement of the independence of a country by a state formerly exercising sovereignty (1824). Meaning "a knowing again" is from 1798.
recognizance (n.): early 14c., reconisaunce, "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). Related: Recognizant.
recognization (n.): "act of recognizing," 1550s, from recognize + -ation.
recognize (v.): early 15c., "resume possession of land," back-formation from recognizance, or else from Old French reconoiss-, stem of reconoistre "to know again, identify, recognize," from Latin recognoscere "acknowledge, recall to mind, know again; examine; certify," from re- "again" (see re-) + cognoscere "to get to know, recognize" (see cognizance). Meaning "know again, recall or recover the knowledge of, perceive an identity with something formerly known or felt" first recorded 1530s. Related: Recognized; recognizing.
recoil (v.): early 13c. (transitive) "force back, drive back," from Old French reculer "to go back, give way, recede, retreat" (12c.), from Vulgar Latin *reculare, from Latin re- "back" (see re-) + culus "backside, bottom, fundament." Meaning "shrink back, retreat" is first recorded c. 1300; and that of "spring back" (as a gun) in 1520s. Related: Recoiled; recoiling.
recoil (n.): c. 1300, "retreat," from Old French recul "recoil, backward movement, retreat," from reculer (see recoil (v.)). Meaning "back-kick of a firearm" is from 1570s.
recollect (v.): "remember, recover knowledge of," 1550s, from Latin recollectus, past participle of recolligere, literally "to collect again," from re- "again" (see re-) + colligere "gather" (see collect). Related: Recollected; recollecting. The pronunciation is based on recollection.
recollection (n.): 1590s, "a gathering together again," from French récollection (14c.) or directly from Medieval Latin recollectionem (nominative recollectio), noun of action from past participle stem of recolligere (see recollect). Meaning "act of recalling to memory" is from 1680s; a thing or scene so recalled, from 1781.
recombinant (adj.): 1942, from recombine + -ant.
recombination (n.): 1791, from re- + combination.
recombine (v.): 1630s, from re- + combine (v.). Related: Recombined; recombining.
recommence (v.): late 15c., from Old French recommencier "begin again, start afresh" (11c.), from re- "back, again" (see re-) + commencer (see commence). Related: Recommenced; recommencing.
recommend (v.): late 14c., "praise, present as worthy," from Medieval Latin recommendare, from Latin re-, here probably an intensive prefix, or else from a sense now obscure (see re-), + commendare "commit to one's care, commend" (see commend). Meaning "advise as to action, urge (that something be done)" is from 1746. Related: Recommended; recommending.
recommendation (n.): early 15c., "action of commending oneself to another," from Old French recommendation (Modern French recommandation), from Medieval Latin recommendationem (nominative recommendatio), noun of action from past participle stem of recommendare (see recommend). Meaning "act of recommending (someone or something) as worthy" is from 1570s. Letter of recommendation is from late 15c.
recommission (v.): 1781, in reference to British Navy ships, from re- "back, again" + commission (v.). Related: Recommissioned; recommissioning.
recommit (v.): 1620s, from re- "again" + commit (v.). Related: Recommitted; recommitting.
recompense (n.): early 15c., from Middle French recompense (13c.), related to recompenser "make good, recompense" from Late Latin recompensare (see recompense (v.)).
recompense (v.): c. 1400, "to redress," from Middle French recompenser (14c.) and directly from Medieval Latin recompensare "to reward, remunerate," from Latin re- "again" (see re-) + compensare "balance out," literally "weigh together" (see compensate). From early 15c. as "to compensate." Related: Recompensed; recompensing.
recon: military slang shortening; 1918 for reconnaissance (n.); 1966 for reconnoitre (v.).
reconceptualize (v.): 1969, from re- + conceptualize. Related: Reconceptualized; reconceptualizing.
reconcilable (adj.): 1610s, from reconcile + -able.
reconcile (v.): mid-14c., of persons, from Old French reconcilier (12c.) and directly from Latin reconcilare "to bring together again; regain; win over again, conciliate," from re- "again" (see re-) + concilare "make friendly" (see conciliate). Reflexive sense is recorded from 1530s. Meaning "to make (discordant facts or statements) consistent" is from late 14c. Intransitive sense of "become reconciled" is from 1660s. Related: Reconciled; reconciling.
reconciliation (n.): mid-14c., from Old French reconciliacion (14c.) and directly from Latin reconciliationem (nominative reconciliatio) "a re-establishing, a reconciling," noun of action from past participle stem of reconciliare (see reconcile).
recondite (adj.): 1640s, "removed or hidden from view," from Old French recondit, from Latin reconditus, past participle of recondere "store away, hide, conceal, put back again, put up again, lay up," from re- "away, back" (see re-) + condere "to store, hide, put together," from con- "together" (see con-) + -dere "to put, place," comb. form of dare "to give" (see date (n.1)). Meaning "removed from ordinary understanding, profound" is from 1650s; of writers or sources, "obscure," it is recorded from 1817.
recondition (v.): also re-condition, 1850, from re- "back, again" + condition (v.). Related: Reconditioned; reconditioning.
reconfigure (v.): 1964, from re- + configure. Related: Reconfigured; reconfiguring.
reconnaissance (n.): 1810, from French reconnaissance "act of surveying," literally "recognition," from Old French reconoissance "recognition, acknowledgement" (see recognizance).
reconnect (v.): 1752, from re- + connect (v.). Related: Reconnected; reconnecting.
reconnoiter (v.): also reconnoitre, 1707, "make a survey," from older French reconnoitre (Modern French reconnaître), from Old French reconoistre "to identify" (see recognize).
reconquer (v.): 1580s, from Middle French reconquerre (12c.), from re- "again, back" (see re-) + conquerre (see conquer). Related: Reconquered; reconquering.
reconquest (n.): 1540s, from Middle French reconqueste (16c., Modern French reconquête), cognate with Spanish reconquista; see re- + conquest.
reconsider (v.): 1570s, from French reconsidérer and also from re- "back, again" + consider. Related: Reconsidered; reconsidering.
reconsideration (n.): 1650s, from re- "again" + consideration.
reconstitute (v.): 1790, from re- "back, again" + constitute (v.). Related: Reconstituted; reconstituting.
reconstruct (v.): 1768, "to build anew," from re- "back, again" + construct (v.). Meaning "to restore (something) mentally" is attested from 1862. Related: Reconstructed; reconstructing.
reconstruction (n.): 1791, "action or process of reconstructing," from re- + construction. In U.S. political history sense (usually with a capital R-), from 1865. It had been used during the American Civil War in reference to reconstitution of the union.
reconvene (v.): 1640s, from re- + convene and from Medieval Latin reconvenire. Related: Reconvened; reconvening; reconvention.