Online Etymology Dictionary

laches (n.): "negligence in performance of legal duty," 1570s, earlier simply "slackness, negligence, want of zeal" (late 14c.), from Anglo-French laches, Old French lachesse "lawlessness, remissness," from Old French lasche "lax, remiss" (Modern French lâche), verbal adjective from lascher, from Vulgar Latin *lascare, classical laxare "to slacken, relax," from laxus "loose; yielding; indulgent" (see lax). Compare riches.
lachrymal (adj.): also lachrimal, lacrymal, early 15c., from Medieval Latin lacrimalis "pertaining to tears," from Latin lacrima, lacryma "a tear" (see lachrymose). The corrupted spelling with -ch- began in Medieval Latin. Hence French larme, Spanish lagrima "a tear," French larmoyer "to shed tears."
lachrymose (adj.): also lacrymose, 1660s, "tear-like," from Latin lacrimosus "tearful, sorrowful, weeping," also "causing tears, lamentable," from lacrima, lacryma "a tear," a dialect-altered borrowing of Greek dakryma "a tear," from dakryein "to shed tears, weep, lament with tears," from dakry "a tear" (from PIE *dakru- "tear;" see tear (n.1)). Meaning "given to tears, tearful" is first attested 1727; meaning "of a mournful character" is from 1822. Related: Lachrymosely.

The -d- to -l- alteration in Latin is the so-called "Sabine -L-"; compare Latin olere "smell," from root of odor, and Ulixes, the Latin form of Greek Odysseus. The Medieval Latin practice of writing -ch- for -c- before Latin -r- also altered anchor, pulchritude, sepulchre. The -y- is pedantic, from the former belief that the word was pure Greek. Earlier in the same sense was lachrymental (1620s). Middle English had lacrymable "tearful" (mid-15c.).
laciniate (adj.): in botany, "irregularly cut in narrow lobes, jagged," literally "adorned with fringes," 1760, from Latin lacinia "a flap" (see lacerate).
lack (n.): c. 1300, "absence, want; shortage, deficiency," not found in Old English, of uncertain origin. Perhaps it is from an unrecorded Old English *lac, or else borrowed from Middle Dutch lak "deficiency, fault;" in either case probably from Proto-Germanic *lek- (source also of Old Frisian lek "disadvantage, damage," Old Norse lakr "lacking" (in quality), "deficient" (in weight)), from PIE *leg- (2) "to dribble, trickle" (see leak (v.)). Middle English also had lackless "without blame or fault."
lack (v.): "be wanting or deficient" (intransitive), late 12c., perhaps from Middle Dutch laken "to be wanting," from lak (n.) "deficiency, fault," or an unrecorded native cognate word (see lack (n.)). Transitive sense "be in want of" is from early 13c. Related: Lacked; lacking.
lackadaisical (adj.): "sentimentally woebegone" [Century Dictionary], 1768, lack-adaysical (Sterne), from interjection lackadaisy "alas, alack" (1748), a ludicrous alteration of lack-a-day (1690s), an exclamation of sorrow or regret, from alack the day (1590s). Hence, "given to crying 'lack-a-day,' vapidly sentimental." Sense probably altered by influence of lax. Related: Lackadaisically.
lackey (n.): 1520s, "footman, running footman, valet," from Middle French laquais "foot soldier, footman, servant" (15c.), a word of unknown origin; perhaps from Old Provençal lacai, from lecai "glutton, covetous," from lecar "to lick." The alternative etymology is that it comes via Old French laquay, from Catalan alacay, from Arabic al-qadi "the judge." Yet another guess traces it through Spanish lacayo, from Italian lacchè, from Modern Greek oulakes, from Turkish ulak "runner, courier." This suits the original sense better, but OED says Italian lacchè is from French. Sense of "servile follower" appeared 1580s. As a political term of abuse it dates from 1939 in communist jargon.
lackluster (adj.): also lack-luster, c. 1600, "dull, wanting brightness" (originally of eyes), first attested in "As You Like It," from lack (v.) + luster (n.1). Such combinations with lack- were frequent once: Shakespeare alone also has lack-love, lack-beard, lack-brain, lack-linen. Outside Shakespeare there was lackland (1590s), of a landless man; lack-Latin (1530s), of an ignorant priest; lack-learning (1590s), lack-wit (Dryden), lack-thought (1829), lack-life (1889), and the comprehensive lack-all (1850).
lacklustre (adj.): also lack-lustre, chiefly British English spelling of lackluster (q.v.); for spelling, see -re.
Laconian (adj.): "of or pertaining to the region around Sparta," 1570s, from Latin Laconia (from Greek Lakonia; see laconic) + -ian. As a noun from c. 1600.
laconic (adj.): "concise, abrupt," 1580s, literally "of or pertaining to the region around ancient Sparta in Greece, probably via Latin Laconicus "of Laconia," from Greek Lakonikos "Laconian, of Laconia," adjective from Lakon "person from Lakonia," the district around Sparta in southern Greece in ancient times, whose inhabitants famously cultivated the skill of saying much in few words. When Philip of Macedon threatened them with, "If I enter Laconia, I will raze Sparta to the ground," the Spartans' reply was, "If." An earlier form was laconical (1570s). Related: Laconically.
Lacoste: Paris-based high-end apparel company, founded 1933, named for company co-founder René Lacoste (1904-1996).
lacquer (n.): 1570s, "dye obtained from lac;" 1670s as "gold-colored solution of shellac," from obsolete French lacre, name for a kind of sealing wax, from Portuguese lacre, unexplained variant of lacca "resinous substance," from Arabic lakk, from Persian lak (see lac).
lacquer (v.): "cover or coat with laqueur," 1680s, from lacquer (n.). Related: Lacquered; lacquering.
lacrosse (n.): 1850, American English, from Canadian French jeu de la crosse (18c.), literally "game of the hooked sticks," from crosse "hooked stick," such as that used in the game to throw the ball. This French word is, perhaps via a Gallo-Romance *croccia, from Proto-Germanic *kruk- (see crook (n.)). Originally a North American Indian game; the native name is represented by the Ojibwa (Algonquian) verb baaga'adowe "to play lacrosse." Modern form and rules of the game were laid down 1860 in Canada.
lacrymatory (n.): "small, slender glass vessel," of a type found in ancient sepulchers, 1650s, from Medieval Latin lacrimatorium, noun use of neuter of adjective lacrimatorius "pertaining to tears," from Latin lacrima "a tear" (see lachrymose). "It seems established that in some of them, at least, the tears of friends were collected to be buried with the dead" [Century Dictionary]. As an adjective 1849; the older adjective is lacrymary "designed to contain tears" (1705).
lactate (v.): "secrete milk from the breasts," 1889, probably a back-formation from lactation. The Latin verb was lactare. Related: Lactated; lactating.
lactate (n.): salt of lactic acid, 1790, from French (1789), from stem of lactic + -ate (1).
lactation (n.): 1660s, "process of suckling an infant," from French lactation, from Late Latin lactationem (nominative lactatio) "a suckling," noun of action from past participle stem of lactare "suckle," from lac (genitive lactis) "milk," from PIE root *glakt- (see glacto-). Meaning "process of secreting milk from the breasts" first recorded 1857. Related: Lactational.
lacteal (adj.): 1650s, "pertaining to milk," earlier "milk-white" (1630s), from Latin lacteus "milky" (from lac "milk;" see lacto-) + -al (1). Other 17c. attempts at an adjective in English yielded lactary, lactaceous, lacteant, lacteous, lactescent, and, in a specialized sense ("milk-producing"), lactific.
lactescence (n.): "milky appearance," 1680s, from lactescent "becoming milky" (1660s), from Latin lactescentem (nominative lactescens), present participle of lactescere, inchoative of lactere "to be milky," from lac "milk" (see lacto-).
lactic (adj.): 1790, "procured from milk," in the chemical name lactic acid, which is so called because it was obtained from sour milk. From French lactique, from Latin lactis, genitive of lac "milk" (see lacto-) + French -ique (see -ic).
lactivorous (adj.): 1824; see lacto- "milk" + -vorous "devouring."
lacto-: before vowels, lac-, word-forming element used in chemistry and physiology from 19c. and meaning "milk," from Latin lac (genitive lactis) "milk," from PIE root *glakt-, source also of Greek gala, genitive galaktos, "milk." This and the separate root *melg- (see milk (n.)) account for words for "milk" in most of the Indo-European languages. The absence of a common word for it is considered a mystery. Middle Irish lacht, Welsh llaeth "milk" are loan words from Latin.
lactose (n.): sugar from milk, 1843, from French, coined 1843 by French chemist Jean Baptiste André Dumas (1800-1884) from Latin lac (genitive lactis) "milk" (see lacto-) + chemical suffix -ose (2).
lacuna (n.): "blank or missing portion in a manuscript," 1660s, from Latin lacuna "hole, pit," figuratively "a gap, void, want," diminutive of lacus "pond, lake; hollow, opening" (see lake (n.1)). The Latin plural is lacunae. The word has also been used in English from c. 1700 in the literal Latin sense in anatomy, zoology, botany. The adjectival forms have somewhat sorted themselves: Mathematics tends to use lacunary (1857), natural history lacunose (1816), and lacunar (n.) is used in architecture of paneled ceilings (1690s), so called for their sunken compartments. Leaving lacunal (1846) for the manuscript sense.
lacunae: plural of lacuna (q.v.).
lacustrine (adj.): "of or pertaining to lakes," 1826, irregularly formed from Latin lacus "lake" (see lake (n.1)).
lacy (adj.): 1804, from lace (n.) in the decorative sense + -y (2).
lad (n.): c. 1300, ladde "foot soldier," also "young male servant" (attested as a surname from late 12c.), possibly from a Scandinavian language (compare Norwegian -ladd, in compounds for "young man"), but of obscure origin in any case. OED hazards a guess on Middle English ladde, plural of the past participle of lead (v.), thus "one who is led" (by a lord). Liberman derives it from Old Norse ladd "hose; woolen stocking." "The development must have been from 'stocking,' 'foolish youth' to 'youngster of inferior status' and (with an ameliorated meaning) to 'young fellow.'" He adds, "Words for socks, stockings, and shoes seem to have been current as terms of abuse for and nicknames of fools." Meaning "boy, youth, young man" is from mid-15c.
ladder (n.): Old English hlæder "ladder, steps," from Proto-Germanic *khlaidri (source also of Old Frisian hledere, Middle Dutch ledere, Old High German leitara, German Leiter), from PIE root *klei- "to lean" (source also of Greek klimax "ladder;" see lean (v.)). In late Old English, rungs were læddrestæfæ and the side pieces were ledder steles. The belief that bad things happen to people who walk under ladders is attested from 1787, but its origin likely is more scientific than superstitious.
ladder-back (adj.): 1898 as a type of chair, from ladder (n.) + back (n.).
laddie (n.): 1540s, Scottish diminutive form of lad, also a term of endearment.
laddish (adj.): 1841, from lad (n.) + -ish.
lade (v.): Old English hladan (past tense hlod, past participle gehladen) "to load, heap up, burden" (the general Germanic sense), also "to draw or take up water" (a meaning peculiar to English), from Proto-Germanic *hlathan- (source also of Old Norse hlaða "to pile up, load, especially a ship," Old Saxon hladan, Middle Dutch and Dutch laden, Old Frisian hlada "to load," Old High German hladen, German laden), from PIE *kla- "to spread out flat" (source also of Lithuanian kloti "to spread," Old Church Slavonic klado "to set, place").

In modern use restricted to the loading of ships; past participle laden was active in the language longer, but in 20c. was displaced by loaded (but a distinct word in the literal sense would be useful) except in particular phrases. Compare Lading.
laden (adj.): "loaded, weighted down," 1590s, adjective from the original past participle of lade.
ladies (n.): plural of lady (q.v.). Ladies' night (1880) originally was any event to which women were invited at an all-male club.
Every succeeding occasion is usually said to be "the best ever," but for true pleasure, comfort and genuine enjoyment it is doubtful if any occasion has been more truly "the best ever" than the ladies' night of the Paint, Oil and Varnish Club of Chicago, which was given in the Crystal ballroom of the Blackstone Hotel, Chicago, Thursday evening January 26. ["Paint, Oil and Drug Review," Feb. 1, 1911]
Ladin (n.): Rhaeto-Romanic dialect spoken in Switzerland and Tyrol, 1873, from Rhaeto-Romanic Ladin (Italian Ladino), from Latin Latinus "Latin" (see Latin (adj.)).
lading (n.): early 15c., "act of loading a boat," verbal noun from lade (v.). From 1520s as "that which constitutes a load."
Ladino (n.): 1889, a jargon of Spanish mixed with Hebrew, Arabic, and other elements, written in Hebrew characters, spoken by Sephardim in Turkey, Greece, etc.; from Spanish Ladino "Latin," from Latin Latinus (see Latin. The Spanish word also had a sense of "sagacious, cunning, crafty," on the notion of "knowing Latin." The Spanish word also appeared in American English in its Central American sense, "mestizo, lighter-skinned mixed race person" (1850).
ladle (n.): "large, long-handled spoon for drawing liquids," late Old English hlædel "ladle" (glossing Latin antlia), from hladan "to load; to draw up water" (see lade) + instrumental suffix -el (1) expressing "appliance, tool" (compare handle (n.)).
ladle (v.): "to lift or dip with a ladle," 1758, from ladle (n). Related: Ladled; ladling.
lady (n.): c. 1200, lafdi, lavede, from Old English hlæfdige (Northumbrian hlafdia, Mercian hlafdie), "mistress of a household, wife of a lord," apparently literally "one who kneads bread," from hlaf "bread" (see loaf (n.)) + -dige "maid," which is related to dæge "maker of dough" (which is the first element in dairy; see dey (n.1)). Also compare lord (n.)). Century Dictionary finds this etymology "improbable," and OED rates it "not very plausible with regard to sense," but no one seems to have a better explanation.

The medial -f- disappeared 14c. The word is not found outside English except where borrowed from it. Sense of "woman of superior position in society" is c. 1200; that of "woman whose manners and sensibilities befit her for high rank in society" is from 1861 (ladylike suggesting this sense is attested from 1580s, and ladily from c. 1400). Meaning "woman chosen as an object of chivalrous love" is from early 14c. Used commonly as an address to any woman since 1890s.

Applied since Old English to the Holy Virgin, hence many extended usages in plant names, place names, etc., from genitive singular hlæfdigan, which in Middle English merged with the nominative, so that lady- often represents (Our) Lady's, as in ladybug. Lady Day (late 13c.) was the festival of the Annunciation of the Virgin Mary (March 25). Ladies' man first recorded 1784; lady-killer "man supposed to be dangerously fascinating to women" is from 1811. Lady of pleasure recorded from 1640s. Lady's slipper as a type of orchid is from 1590s.
lady-love (n.): "woman who is the object of one's affections," 1733; see lady + love (n.).
ladybird (n.): also lady-bird, 1590s, "sweetheart," a term of endearment, from lady + bird (n.2). As the name of a type of beetle, 1670s, the earlier form of ladybug.
ladybug (n.): also lady-bug, 1690s, from lady + bug (n.). The "lady" is the Virgin Mary (compare German cognate Marienkäfer). In Britain, usually ladybird or lady-bird (1670s), supposedly through aversion to the word bug due to overtones of sodomy, however this seems to be the older form of the word. Also known 17c.-18c. as lady-cow or lady-fly.
ladyfinger (n.): also lady-finger, used of anything long, slender, and suggestive of grace, 1660s, originally of a type of plant; 1820 in reference to a kind of long, slender confection; see lady + finger (n.).
ladylike (adj.): also lady-like, 1580s, "refined, well-bred, courteous;" see lady + like (adj.). Middle English had ladily "queenly, exalted" (late 14c.).
ladyship (n.): "rank or dignity of a lady," early 13c.; see lady + -ship.