Online Etymology Dictionary

leech (n.1): "bloodsucking aquatic worm," from Old English læce (Kentish lyce), of unknown origin (with a cognate in Middle Dutch lake). Commonly regarded as a transferred use of leech (n.2), but according to OED the Old English forms suggest this is a distinct word, which has been assimilated to leech (n.2) by folk etymology. Figuratively applied to human parasites since 1784.
leech (v.): "to cure, heal," c. 1200, from Old English also had a verb læcnian, from the source of leech (n.2). Meaning "to apply leeches medicinally" is from 1802 (implied in leeching), from leech (n.1). Related: Leeched.
leechcraft (n.): "art of healing," Old English læcecræft; see leech (2) + craft (n.). Old English also had læcedom "medicine." A later word for it was leechery (c. 1600).
Leeds: city in England, 16c., earlier Ledes (1086), from Old English Loidis (8c.) "(district of) the people beside the river Lat'" (perhaps an earlier name of the river Aire.
leek (n.): pungent bulbous culinary herb of the genus Allium, related to the onion, long the national badge of the Welsh, Old English læc (Mercian), leac (West Saxon) "leek, onion, garlic," from Proto-Germanic *lauka- (source also of Old Norse laukr "leek, garlic," Danish løg, Swedish lök "onion," Old Saxon lok "leek," Middle Dutch looc, Dutch look "leek, garlic," Old High German louh, German Lauch "leek"). No certain cognates outside Germanic; Finnish laukka, Russian luk-, Old Church Slavonic luku are said to be from Germanic. Also the final element in garlic.
leer (n.): "a significant glance, amorous or malign or both," 1590s, from leer (v).
leer (v.): 1520s, "to look obliquely" (since 18c. usually implying a lustful, wolfish, malicious intent), probably from Middle English noun ler "cheek," from Old English hleor "the cheek, the face," from Proto-Germanic *khleuzas "near the ear," from *kleuso- "ear," from PIE root *kleu- "to hear" (see listen). If so, the notion is probably of "looking askance" (compare the figurative development of cheek). Related: Leered; leering.
leery (adj.): "knowing, wide-awake, untrusting, suspicious, alert," 1718, originally slang, with -y (2), but otherwise of unknown origin. Perhaps from dialectal lere "learning, knowledge" (see lore), or from leer (v.) in a now-obscure sense "walk stealthily with averted looks, sneak away" (1580s). OED suggests connection with archaic leer (adj.) "empty, useless," a general Germanic word (cognate with German leer, Dutch laar), of unknown origin.
lees (n.): "dregs, sediment of wine or any liquor," late 14c., from Old French lies, plural of lie "dregs, sediment," which is probably from Celtic *leg-ya- (compare Old Irish lige "a bed, a lying"), from PIE root *legh- "to lie" (see lie (v.2)).
leet (n.1): in reference to special court proceedings, late 13c., from Anglo-French lete, Anglo-Latin leta, of unknown origin; OED suggests possible connection to let (v.).
leet (n.2): ASCII alternative alphabet used mostly in Internet chat, by 1997, derived from elite (adj.), and sometimes the word also was used as an adjective in that sense in online gaming.
leeward (adj.): "situated away from the wind, on the side opposite the weather side of a ship, pertaining to the quarter toward which the wind blows," 1660s, from lee + -ward. Also as an adverb. Similar formation in Dutch lijwaarts, German leewärts, Swedish lävart. The Leeward Islands are so called in reference to prevailing northeasterly trade winds.
leeway (n.): also lee-way, 1660s, "sideways drift of a ship in her course caused by wind, deviation from true course by drifting to leeward," from lee + way (n.). Applied to loss of progress in general from 1827. Figurative meaning "extra space" is by 1835.
left: "remaining," past tense and past participle of leave (v.).
left (adj.): c. 1200, "opposite of right," probably from Kentish and northern English forms of Old English *lyft "weak; foolish" (in lyft-adl "lameness, paralysis"). Compare East Frisian luf, Dutch dialectal loof "weak, worthless").

Sense of "opposite of right" is from the left being usually the weaker hand), a derived sense also found in cognate Middle Dutch and Low German luchter, luft. Compare Lithuanian kairys "left" and Lettish kreilis "left hand" both from a root that yields words for "twisted, crooked."

The usual Old English winstre/winestra "left" (adj.); "left hand," literally "friendlier," a euphemism used superstitiously to avoid invoking the unlucky forces connected with the left side (compare sinister). The Kentish word itself might have been originally a taboo replacement, if instead it represents PIE root *laiwo- "considered conspicuous" (represented in Greek laios, Latin laevus, and Russian levyi). Greek also uses a euphemism for "left," aristeros "the better one" (compare also Avestan vairyastara- "to the left," from vairya- "desirable").

Meaning "being on the left-hand side" is from c. 1300. As an adverb from early 14c. For political senses, see left (n.). Used since at least c. 1600 in various senses of "irregular, illicit;" earlier proverbial sense was "opposite of what is expressed" (mid-15c.), for example over the left (shoulder) "not at all," added to a statement to negate or neglect what was just said (1705). To have two left feet "be clumsy" is attested by 1902.

Phrase out in left field "out of touch with pertinent realities" is attested from 1944, from the baseball fielding position that tends to be far removed from the play (left field in baseball attested by 1867). The Parisian Left Bank (of the River Seine) has been associated with intellectual and artistic culture since at least 1893.

German link, Dutch linker "left" are said to be not directly related to these, being instead from Old High German slinc and Middle Dutch slink "left," related to Swedish linka "limp," slinka "dangle," and Old English slincan "crawl" (Modern English slink).
left (n.): c. 1200, "the left-hand side, the side opposite the right," from left (adj.). In military formations with reference to the center; of river banks it implies going in the direction the current flows; in an assembly in reference to the seat of the presiding officer; in baseball in reference to the point of view of the batter. Political sense "the democratic or liberal party" arose from the custom of assigning those members of a legislative body to the left side of a chamber. This usage is first attested in English in 1837 (by Carlyle, in reference to the French Revolution), and probably is a loan-translation of French la gauche (1791), said to have originated during the seating of the French National Assembly in 1789 in which the nobility took the seats on the President's right and left the Third Estate to sit on the left. The term became general in U.S. and British political speech c. 1900. Century Dictionary and OED 2nd ed. both refer to this as primarily in reference to continental European politics.
left wing (n.): also (as an adjective) left-wing, 1871 in the political sense (1530s in a military formation sense), from left (adj.) + wing (n.). Related: Left-winger.
left-handed (adj.): late 14c., of persons, "having the left hand stronger or more capable than the right;" 1650s of tools, etc., "designed for use with the left hand," from left (adj.) + -handed. In 15c. it also could mean "maimed." Sense of "underhanded" is from early 17c., as in left-handed compliment (1787, also attested 1855 in pugilism slang for "a punch with the left fist"), as is that of "illicit" (as in left-handed marriage, for which see morganatic; 17c. slang left-handed wife "concubine"). Related: Left-handedly; left-handedness.
left-hander (n.): 1834, "a blow with the left hand," 1871, "left-handed person," from left hand.
left-wing (n.): also (as an adjective) leftwing; 1530s of armies, 1882 in team sports, 1884 in politics; see left (adj.) + wing (n.).
leftish (adj.): 1934, in the political sense, from left (adj.) + -ish. Related: Leftishness.
leftism (n.): 1917, from left in the political sense + -ism.
leftist (adj.): 1897, from left in the political sense + -ist.
leftover (adj.): also left-over, "remaining, not used up," 1890, from left + over. The noun meaning "something left over" is from 1891; leftovers "excess food after a meal" (especially if re-served later) is from 1878; in this sense Old English had metelaf.
leftward (adv.): "to or toward the left or the left-hand side," late 15c., from left (adj.) + -ward. Related: Leftwards.
lefty (n.): "left-handed person," 1886, American English, baseball slang, from left (adj.) + -y (3). Political sense by 1935.
leg (v.): "to use the legs; walk or run," c. 1500 (from the beginning usually with it); from leg (n.).
leg (n.): late 13c., from a Scandinavian source, probably Old Norse leggr "a leg, bone of the arm or leg," from Proto-Germanic *lagjaz (cognates Danish læg, Swedish läg "the calf of the leg"), a word with no certain ulterior connections. Perhaps from a PIE root meaning "to bend" [Buck]. For Old Norse senses, compare Bein, the German word for "leg," in Old High German "bone, leg" (see bone (n.)). Replaced Old English shank (n.), itself also perhaps from a root meaning "crooked."

Distinguished from an arm, leg, or fin in being used for support. Of triangle sides from 1650s (translating Greek skelos, literally "leg"). Extended to furniture supports from 1670s. Meaning "part of pants which cover the leg" is from 1570s. By 1870s the as an adjective it had a salacious suggestion of artistic displays focused on the female form, such as leg-piece in theater jargon, leg-business as slang for "ballet."

The meaning "a part or stage of a journey or race" (1920) is from earlier sailing sense of "a run made by a ship on a single tack when beating to windward" (1867), which was usually qualified as long leg, short leg, etc. Slang phrase shake a leg is attested from 1869 as "dance," 1880 as "hurry up." To be on (one's) last legs "at the end of one's life" is from 1590s, the notion is of something that serves one for support and keeps one moving. To take leg bail was old slang for "run away" (1774).
leg up (n.): "an aid, a boost," 1837, from leg (n.) + up (adv.).
leg-lock (n.): 1848, "chains for the legs," from leg (n.) + lock (n.1). As a hold in wrestling, from 1886.
leg-man (n.): "assistant who does leg work," 1923; see leg (n.)).
leg-rest (n.): 1833, from leg (n.) + rest (n.1) "support on which something rests."
leg-room (n.): also legroom, 1846 (in reference to carriages), from leg (n.) + room (n.).
leg-warmer (n.): 1974, from leg (n.) + agent noun from warm (v.). Related: Leg-warmers.
leg-work (n.): also legwork, 1891, from leg (n.) + work (n.). Originally news reporter slang for an assignment that promised more walking than copy.
legacy (n.): late 14c., legacie, "body of persons sent on a mission," from Medieval Latin legatia, from Latin legatus "ambassador, envoy, deputy," noun use of past participle of legare "send with a commission, appoint as deputy, appoint by a last will" (see legate).

Sense of "property left by will, a gift by will" appeared in Scottish mid-15c. Legacy-hunter is attested from 1690s. French legs "a legacy" is a bad spelling of Old French lais (see lease (n.)). French legacie is attested only from 16c.
legal (adj.): mid-15c. "of or pertaining to the law," from Old French légal "legal" (14c.) or directly from Latin legalis "pertaining to the law," from lex (genitive legis) "an enactment; a precept, regulation, principle, rule; formal proposition for a law, motion, bill; a contract, arrangement, contrivance. This probably is related to legere "to gather" (see lecture (n.)). Perhaps the noun is from the verb on the notion of "a collection of rules," but de Vaan seems to imply that the evolution is the reverse:
The verb legare and its compounds all have a meaning which involves a 'task, assignment,' and can therefore be interpreted as derivatives of lex 'law.' The [Proto-Italic] root noun *leg- 'law' can be interpreted as a 'collection' of rules. Whether the root noun existed already in PIE is uncertain for lack of precise cognates.
Sense of "permitted by law" is from 1640s. Related: Legally. Not etymologically related to law (n.), q.v. The usual Old French form was leial, loial (see leal, loyal). Legal tender "money which the creditor is bound by law to accept" is from 1740 (see tender (n.2)). A legal holiday (1867) is one established by statute or proclamation and during which government business is usually suspended.
legalese (n.): "the language of legal documents," 1914, from legal + language name ending -ese.
legalise (v.): chiefly British English spelling of legealize; for suffix, see -ize. Related: Legalisation; legalised; legalising.
legalistic (adj.): 1843, with -ic + legalist "one who advocates strict adherence to the law," especially in theology (1640s); see legal + -ist. Legalism in theology is attested from 1838.
legality (n.): mid-15c., from Middle French légalité, from Medieval Latin legalitatem (nominative legalitas), from Latin legalis "pertaining to the law" (see legal).
legalization (n.): 1805, noun of action from legalize.
legalize (v.): 1716, from legal + -ize. Related: Legalized; legalizing.
legate (n.): mid-12c., "authorized representative of the Pope," from Old French legat and directly from Latin legatus "ambassador, envoy," originally "provided with a commission," past participle of legare "send as a deputy, send with a commission, charge, bequeath," possibly literally "engage by contract" and related to lex (genitive legis) "contract, law," from PIE root *leg- (see legal). General sense of "ambassador, delegate, messenger of a state or authority" is from late 14c. in English. Related: Legator; legatee; legatine.
legation (n.): c. 1400, "mission of a deputy or envoy," from Old French legation "embassy, mission" and directly from Latin legationem (nominative legatio) "the office of an ambassador," noun of action from past participle stem of legare "send as a deputy" (see legate). From c. 1600 as "body of deputies sent, representatives," 1832 as "official residence of a diplomat."
legato (adv.): in music, "smoothly, without intervals," 1811, from Italian legato, literally "bound," past participle of legare, from Latin ligare "tie" (see ligament). Related: Legatissimo.
legem pone (n.): "payment of money, cash down," 1570s, old slang, from the title in the Anglican prayer-book of the psalm appointed for Matins on the 25th of the month; it was consequently associated especially with March 25, the new year of the old calendar and a quarter day, when payments and debts came due and money changed hands generally. The title is from the first two words of the fifth division of Psalm cxix: Legem pone mihi, Domine, viam justificationum tuarum "Teach me, O Lord, the way of thy statutes."
legend (n.): early 14c., "narrative dealing with a happening or an event," from Old French legende (12c., Modern French légende) and directly from Medieval Latin legenda "legend, story," especially lives of saints, which were formerly read at matins and in refectories of religious houses, literally "(things) to be read," on certain days in church, etc., from Latin legendus, neuter plural gerundive of legere "to read; to gather, pluck, select" (see lecture (n.)).

Extended sense of "nonhistorical or mythical story," with or without saints, wonders, and miracles is first recorded late 14c. Meaning "writing or inscription" (especially on a coin or medal) is from 1610s; on a map, illustration, etc., from 1903. To be a legend in (one's) own time is from 1958.
legendary (adj.): mid-16c., from Medieval Latin legendarius "pertaining to legends," from legenda (see legend). Earlier in English it was a noun meaning "a collection of legends" (1510s).
legerdemain (n.): early 15c., "conjuring tricks, sleight of hand," from Middle French léger de main "quick of hand," literally "light of hand." Léger "light" in weight (Old French legier, 12c.) is from Latin levis "light," from PIE root *legwh- "light, having little weight; easy, agile, nimble" (see lever); it is cognate with Spanish ligero, Italian leggiero "light, nimble" (hence also leger line in music). Main "hand" is from Latin manus (see manual (adj.)).