Online Etymology Dictionary

lactose: sugar from milk, 1858, from Fr., coined by Fr. chemist Marcelin-Pierre-Eugène Berthelot (1827-1907) from L. lac "milk" (see lactation) + suffix -ose.
lacuna: 1660s, "blank or missing portion in a manuscript," from L. lacuna "hole, pit," dim. of lacus "pond, lake" (see lake (1)). The Latin plural is lacunae.
lacunae: plural of lacuna (q.v.).
lacy: 1804, from lace + -y (2).
lad: c.1300, ladde "foot soldier," also "young male servant" (attested as a surname from c.1100), possibly from a Scandinavian language (cf. Norw. -ladd, in compounds for "young man"), but of obscure origin in any case. OED hazards a guess on M.E. ladde, plural of the pp. of lead (v.), thus "one who is led" (by a lord). Meaning "boy, youth, young man" is from mid-15c. Scottish form laddie, a term of endearment, attested from 1540s.
ladder: O.E. hlæder, from P.Gmc. *khlaidri (cf. O.Fris. hledere, M.Du. ledere, O.H.G. leitara, Ger. Leiter), from PIE base *khli- "to lean" (cf. Gk. klimax "ladder;" see lean (v.)). The belief that walking under one brings bad luck is attested from 1787, but its origin likely is more pragmatic than symbolic.
lade: O.E. hladan (past tense hlod, pp. gehladen) "to load, heap" (the general Gmc. sense), also "to draw water" (a meaning peculiar to Eng.), from P.Gmc. *khlad- (cf. O.N. hlaða, O.Fris. hlada, O.H.G. hladen, Ger. laden), from PIE *klat- (cf. Lith. kloti "to spread," O.C.S. klado "to set, place").
laden: 1590s, adj. from the original pp. of lade.
ladies: plural of lady (q.v.).
Ladin: 1877, Rhaeto-Romanic dialect spoken in Switzerland and Tyrol, from L. Latinus "Latin."
lading: c.1500, from lade.
Ladino: 1889, Spanish mixed with Hebrew, Arabic, and other elements, written in Heb. characters, spoken by Sephardim in Turkey, Greece, etc. From Sp. Ladino "sagacious, cunning crafty," originally "knowing Latin, Latin," from L. Latinus. The Sp. word also has appeared in 19c. Amer.Eng. in its senses "vicious horse" and, in Central America, "mestizo, white person."
ladle: "large, long-handled spoon for drawing liquids," O.E. hlædel, from hladan "to load" (see lade) + -le, suffix expressing "appliance, tool" (cf. shovel). The verb is first recorded 1520s. Related: Ladled.
lady: M.E. lafdi, lavede, ladi, from O.E. hlæfdige "mistress of a household, wife of a lord," lit. "one who kneads bread," from hlaf "bread" (see loaf) + -dige "maid," related to dæge "maker of dough" (see dey (1); also compare lord). Not found outside English except where borrowed from it. Sense of "woman of superior position in society" is c.1200; "woman whose manners and sensibilities befit her for high rank in society" is from 1861 (ladylike in this sense is from 1580s). Meaning "woman as an object of chivalrous love" is from late 14c. Used commonly as an address to any woman since 1890s. Applied in O.E. to the Holy Virgin, hence many extended usages in plant names, etc., from gen. sing. hlæfdigan, which in M.E. merged with the nominative, so that lady- often represents (Our) Lady's; e.g. ladybug. Ladies' man first recorded 1784.
ladybug: 1690s, from lady + bug. The "lady" is the Virgin Mary (cf. Ger. cognate Marienkäfer). In Britain, now usually ladybird beetle (1704), through aversion to the word bug, which there has overtones of sodomy.
Laertes: king of Ithaca, father of Odysseus, Gk., lit. "gatherer of the people," from laos "people" + eirein "to fasten together."
lag (v.): "fail to keep pace," 1520s, from earlier adj. meaning "last" (1510s), e.g. lag-mon "last man," possibly from a Scandinavian source (cf. Norw. lagga "go slowly"), or some dialectal version of last, lack, or delay. Related: Lag; lagging. First record of lag time is from 1956.
lager: 1858, Amer.Eng., short for lager beer (1853), from Ger. Lager-bier "beer brewed for keeping," from Lager "storehouse" (see lair) + Bier "beer."
laggard: 1702, from lag (v.) + -ard.
lagniappe: "dividend, something extra," 1849, from New Orleans creole, of unknown origin though much speculated. Originally a bit of something given by New Orleans shopkeepers to customers. Said to be from Amer.Sp. la ñapa "the gift." Klein says this is in turn from Quechua yapa "something added, gift."
We picked up one excellent word -- a word worth travelling to New Orleans to get; a nice, limber, expressive, handy word -- 'lagniappe.' They pronounce it lanny-yap. It is Spanish -- so they said. [Mark Twain, "Life on the Mississippi"]
lagoon: 1612, from Fr. lagune, from It. laguna "pond, lake," from L. lacuna "pond, hole," from lacus "pond" (see lake). Originally in ref. to the region of Venice; applied 1769 to the lake-like stretch of water enclosed in a South Seas atoll.
laic: 1562, from Fr. laique, from L.L. laicus, from Gk. laikos "of or belonging to the people," from laos "people" (see lay (adj.)).
laid: pp. of lay (v.). Laid-up "injured, sick," originally was a nautical term (1769) describing a ship moored in harbor. Laid off "temporarily unemployed" is from 1955. Laid-back "relaxed" is first attested 1973, perhaps in reference to the posture of highway motorcyclists.
laidly: c.1300, Scottish and northern English variant of loathly "hideous, repulsive."
lain: past participle of lie (v.2).
lair: O.E. leger "bed, couch, grave, act or place of lying down," from P.Gmc. *legran (cf. O.N. legr, O.Fris. legor, O.H.G. legar, Ger. Lager, Goth. ligrs "place of lying"), from *leg-, the root of lie (v.2). Meaning "animal's den" is from early 15c.
laird: mid-15c., Scottish and northern England dialectal variant of lord, from M.E. laverd (see lord). Attested as a surname from 1257.
laissez-faire: 1825, also laissez faire, from Fr., lit. "let (people) do (as they think best)," from laissez, imperative of laisser "to let" + faire "to do" (from L. facere; see factitious). From the phrase laissez faire et laissez passer, motto of certain 18c. French economists, chosen to express the ideal of government non-interference in business and industry.
laity: 1540s, "body of people not in religious orders," Anglo-Fr. laite, from lay (adj.).
lake (1): "body of water," c.1200, from O.Fr. lack, from L. lacus "pond, lake," also "basin, tank," related to lacuna "hole, pit," from PIE *lak- (cf. Gk. lakkos "pit, tank, pond," O.C.S. loky "pool, puddle, cistern," O.Ir. loch "lake, pond"). The common notion is "basin." There was a Gmc. form of the word, which yielded cognate O.N. lögr "sea flood, water," O.E. lacu "stream," lagu "sea flood, water," leccan "to moisten" (see leak). The N.Amer. Great Lakes so called from 1660s. Laker "boat made for sailing on the Great Lakes" is from 1887.
lake (2): "deep red coloring matter," 1616, from Fr. laque (see lac), from which it was obtained.
laker: used of people or things associated in various ways with a lake or lakes, including tourists to the English Lake country (1798); the poets (Wordsworth, etc.) who settled in that region (1814); boats on the North American Great Lakes (1887), and a person whose work is on lakes (1838); see lake (-). The U.S. professional basketball team began 1947 as the Minneapolis Lakers, where the name was appropriate; before the 1960-1 season it moved to Los Angeles, but the name was kept.
lam: "flight," as in on the lam, 1897, from a U.S. slang verb meaning "to run off" (1886), of uncertain origin, perhaps somehow from the first element of lambaste, which was used in British student slang for "beat" since 1596; if so, it would give the word the same etymological sense as beat it.
lama: "Buddhist priest of Mongolia or Tibet," 1654, from Tibetan blama "chief, high priest," with silent b-.
Lamarckian: 1846, of or pertaining to Fr. botanist and zoologist J.B.P. Lamarck (1744-1829), especially his view that the process of evolution includes the inheritance of acquired characteristics.
Lamaze: childbirth technique, developed 1940s by Fr. obstetrician Dr. Fernand Lamaze (1891-1957) and named for him.
lamb: O.E. lamb, from P.Gmc. *lambaz (cf. O.N., O.Fris., Goth. lamb, M.H.G. lamp, Ger. lamm "lamb"). Common to the Gmc. languages, but with no known cognates outside them. O.E. plural was lomberu. Applied to persons (especially young Church members, gentle souls, etc.) from late O.E. Also sometimes used ironically for cruel or rough characters (e.g. Kirke's Lambs in wars of 1684-86).
lambada: "sensual Brazilian dance," 1988, from Port., lit. "a beating, a lashing."
lambaste: 1630s, from lam (1590s, ult. from O.N. lemja "to beat, to lame") + baste "to thrash" (see baste). Related: Lambasted; lambasting.
lambent: 1647, from fig. use of L. lambentem (nom. lambens), prp. of lambere "to lick," from PIE base *lab- (cf. Gk. laptein "to sip, lick," O.E. lapian "to lick, lap up, suck").
Lambert: masc. proper name, from French, from Ger. Lambert, from O.H.G. Lambreht, from lant "land" + beraht "bright." O.E. cognate was Landbeorht. The popularity of the name from 12c. is probably due to immigration from Flanders, where St. Lambert of Maestricht was highly venerated. Attested as a surname from mid-12c.
Lambeth: used metonymically for "Church of England, Archbishop of Canterbury," 1859, from the archbishop's palace in Lambeth, a South London borough. The Lambeth Walk was a Cockney song and dance, popularized in Britain 1937 in the revue "Me and my Gal," named for a street in the borough.
lambic: "strong Belgian beer," 1889, related to Fr. alambic "a still" (see alembic).
lamé (n.): "silk interwoven with metallic threads," 1922, from Fr., earlier "thin metal plate" (1586), from M.Fr. lame, from L. lamina, lamna "thin piece or flake of metal."
lame (adj.): O.E. lama. from P.Gmc. *lamon (cf. O.N. lami, Du., O.Fris. lam, Ger. lahm "lame"), "weak-limbed," lit. "broken," from PIE base *lem- "to break" (cf. O.C.S. lomiti "to break," Lith. luomas "lame"). Sense of "socially awkward" is attested from 1942. Verb meaning "to make lame" is attested from c.1300. Related: Lamely; lameness. Lame-brain (n.) is first recorded 1929.
lame duck: mid-18c., "any disabled person or thing;" especially Stock Exchange slang for "defaulter."
A lame duck is a man who cannot pay his differences, and is said to waddle off. [Thomas Love Peacock, "Gryll Grange," 1861]
Sometimes also in naval use for "an old, slow ship." Modern sense of "public official serving out term after an election" is recorded by 1878 in Amer.Eng., from an anecdote published in that year of President Lincoln, who is alleged to have said, "[A] senator or representative out of business is a sort of lame duck. He has to be provided for."
lament (v.): 1530s, back-formation from lamentation. The noun is recorded from 1590s. Related: Lamented; lamenting.
lamentable: early 15c., from Fr. lamentable, from L. lamentabilis, from lamentari (see lamentation). Related: Lamentably.
lamentation: late 14c., from L. lamentationem (nom. lamentatio) "wailing, moaning, weeping," from lamentatus, pp. of lamentari, from lamentum "a wailing," from PIE base *la- "to shout, cry," probably ultimately imitative. Replaced O.E. cwiþan.
Lamentations: Biblical book, late 14c., short for Lamentations of Jeremiah, from L. Lamentationes, from Gk. Threnoi (see lamentation).