Online Etymology Dictionary

lascivious (adj.): mid-15c., from Middle French lascivieux or directly from Late Latin lasciviosus (used in a scolding sense by Isidore and other early Church writers), from Latin lascivia "lewdness, playfulness, frolicsomeness, jolity," from lascivus "lewd, playful, frolicsome, wanton," from PIE *las-ko-, from *las- "to be eager, wanton, or unruly" (cf. Sanskrit -lasati "yearns," lasati "plays, frolics," Hittite ilaliya- "to desire, covet," Greek laste "harlot," Old Church Slavonic laska "flattery," Slovak laska "love," Old Irish lainn "greedy," Gothic lustus, Old English lust "lust"). Related: Lasciviously; lasciviousness. In 17c. also with a verbal form, lasciviate.
laser (n.): 1960, acronym for "light amplification by stimulated emission of radiation," on pattern of 1955 MASER. A corresponding verb, lase, was coined 1962.
lash (n.): c.1300, las "a blow, a stroke," later "flexible part of a whip" (late 14c.), possibly imitative. The verb might be the source of the noun.
lash (v.2): "bind," 1620s, originally nautical, from Middle French lachier, from Old French lacier "to lace" (see lace (v.)). Related: Lashed; lashing.
lash (v.1): "to strike with a whip," c.1300, "to deal a blow;" later "to whip" (late 14c.); see lash (n.). Lash out "to strike out violently" is from 1560s. Related: Lashed; lashing.
lashing (n.): "a beating, flogging," c.1400, verbal noun from lash (v.1).
lass (n.): "young woman," c.1300, probably from a Scandinavian source akin to Old Swedish løsk kona "unmarried woman," but also perhaps related to Old Norse löskr "idle, weak," West Frisian lask "light, thin." Liberman suggests Old Danish las "rag." "Slang words for 'rag' sometimes acquire the jocular meaning 'child' and especially 'girl.'" "Used now only of mean girls" [Johnson, who also has lasslorn "forsaken by his mistress"]. Scottish diminutive lassie first recorded 1725.
lassitude (n.): early 15c., from Middle French lassitude (14c.), from Latin lassitudinem (nominative lassitudo) "faintness, weariness," from lassus "faint, tired, weary," from PIE *led- "slow, weary" (cf. Old English læt "sluggish, slow;" see late (adj.)), from root *le- "to let go, slacken" (see lenient).
lasso: 1807 (v.); 1808 (n.), American English, from Spanish lazo, from Latin laqueum (nominative laqueus) "noose, snare" (see lace (n.)).
last (adj., adv.): "following all others," from Old English latost (adj.) and lætest (adv.), superlative of læt (see late). Cognate with Old Frisian lest, Dutch laatst, Old High German laggost, German letzt. Meaning "most recent" is from c.1200. The noun, "last person or thing," is c.1200, from the adjective. Last hurrah is from the title of Edwin O'Connor's 1956 novel. Last word "final, definitive statement" is from 1650s. A dying person's last words so called by 1740. As an adjective, last-minute attested from 1913. Last-chance (adj.) is from 1962.
last (v.): "endure, go on existing," from Old English læstan "to continue, endure," earlier "accomplish, carry out," literally "to follow a track," from Proto-Germanic *laistjan "to follow a track" (cf. Gothic laistjan "to follow," Old Frisian lasta "to fulfill, to pay (duties)," German leisten "to perform, achieve, afford"), from PIE *leis- "track, furrow."

Related to last (n.), not to last (adj.). Related: Lasted; lasting.
last (n.): "shoemaker's block," from Old English læste, from last "track, footprint, trace," from Proto-Germanic *laist- (cf. Old Norse leistr "the foot," Middle Dutch, Dutch leest "form, model, last," Old High German leist "track, footprint," German Leisten "last," Gothic laistjan "to follow," Old English læran "to teach"); see last (v.).
last-ditch (adj.): "on the last line of defense," 1715, attributed to William of Orange; if so, originally in a Dutch context.
We have no space to enter into the detail of the heroic struggle maintained by the young stadtholder and his faithful Dutchmen; how they laid their country under water, and successfully kept the powerful invader at bay. Once the contest seemed utterly hopeless. William was advised to compromise the matter, and yield up Holland as the conquest of Louis XIV. "No," replied he; "I mean to die in the last ditch." A speech alone sufficient to render his memory immortal. [Agnes Strickland, "Lives of the Queens of England," London, 1847]
lastly (adv.): late 14c., from last (adj.) + -ly (2).
latch (v.): Old English læccan "to grasp or seize," from Proto-Germanic *lakkijanan. Not found in other Germanic languages; probably from PIE *(s)lagw- "to seize" (see analemma). In its original sense the verb was paralleled in Middle English and then replaced by French import catch (v.). Meaning "to fasten with a latch" is mid-15c. Related: Latched; latching.
latch (n.): a fastening for a door, etc., late 13c., probably from latch (v.).
latchkey: also latch-key, 1825, a key to draw back the latch of a door, from latch (n.) + key (n.1). Latchkey child first recorded 1944, American English, in reference to children who come home from school while both parents are at work.
late (adj.): Old English læt "occurring after the customary or expected time," originally "slow, sluggish," from Proto-Germanic *lata- (cf. Old Norse latr "sluggish, lazy," Middle Dutch, Old Saxon lat, German laß "idle, weary," Gothic lats "weary, sluggish, lazy," latjan "to hinder"), from PIE *led- "slow, weary" (cf. Latin lassus "faint, weary, languid, exhausted," Greek ledein "to be weary"), from root *le- "to let go, slacken" (see let (v.)).

The sense of "deceased" (as in the late Mrs. Smith) is from late 15c., from an adverbial sense of "recently." Of women's menstrual periods, attested colloquially from 1962. Related: Lateness. As an adverb, from Old English late.
lateen: mid-18c., phonetic spelling of French latine in voile latine, literally "Latin sail" (see Latin). So called because it was used in the Mediterranean.
lately (adv.): Old English lætlice "slow, sluggish;" see late (adj.) + -ly (2). Meaning "within recent times" is from late 15c., probably a new formation.
latency (n.): 1630s, "condition of being concealed," from latent + -cy. Meaning "delay between stimulus and response" is from 1882; computer sense (latency time) is from 1954.
latent (adj.): mid-15c., "concealed, secret," from Latin latentem (nominative latens) "lying hid, secret, unknown," present participle of latere "to lie hidden," from PIE *laidh-, from root *la- "to be hidden" (cf. Greek lethe "forgetfulness, oblivion," Old Church Slavonic lajati "to lie in wait for"). Meaning "dormant" is from 1680s.
later: comparative of late. Meaning "farewell" is from 1954, U.S. slang, short for see you later.
lateral (adj.): early 15c., from Middle French latéral and directly from Latin lateralis "belonging to the side," from latus (genitive lateris) "side" (see oblate (n.)). As a noun, from 1630s, "a side part." As a type of pass to the side in U.S. football, it is attested from 1934. Related: Laterally.
Lateran: c.1300, popular name of cathedral church of St. John Lateran at Rome, which is built on the site of the palace of the Plautii Laterani, a Roman family. As a papal headquarters, it was the site of five general councils of the Western Church.
latescent (adj.): "tending to become latent," 1836, from Latin latescentem (nominative latescens), present participle of latescere "to hide oneself, be hidden," inchoative of latere (see latent).
latest (adj.): superlative of late. The latest "the news" attested from 1886.
latex (n.): 1660s, "body fluid," from Latin latex (genitive laticis) "liquid, fluid," probably from Greek latax "dregs," from PIE root *lat- "wet" (cf. Middle Irish laith "beer," Welsh llaid "mud, mire," Lithuanian latakas "pool, puddle," Old Norse leþja "filth"). Used 1835 to mean "milky liquid from plants." Meaning "water-dispersed polymer particles" (used in rubber goods, paints, etc.) is from 1937. As an adjective by 1954, in place of clasically correct laticiferous.
lath (n.): late 13c., probably from Old English *læððe, variant of lætt "lath," apparently from a Proto-Germanic *laþþo (cf. Old Saxon, Old Norse latta, Middle Dutch, German latte "lath," Dutch lat, Middle High German lade "plank," which is source of German Laden "counter," hence, "shop"). As a verb, 1530s, from the noun.
lathe (n.): "machine for turning," early 14c., of uncertain origin, probably from a Scandinavian source (cf. Danish drejelad "turning-lathe," Old Norse hlaða "pile of shavings under a lathe," related to hlaða "to load, lade").
lather (n.): Old English lauþr "foam, washing soda," from Proto-Germanic *lauþran (cf. Old Norse lauðr "washing soap, foam"), from PIE *loutro- (cf. Gaulish lautron, Old Irish loathar "bathing tub," Greek louein "to bathe," Latin lavere "to wash"), which is from root *leu(e)- "to wash" + instrumentative suffix *-tro-. The modern noun might be a 16c. redevelopment from the verb. Meaning "violent perspiration" (especially of horses) is from 1650s. Meaning "state of agitation" (such as induces sweating) is from 1839.
lather (v.): Old English laþran, from Proto-Germanic *lauþrjan (cf. Old Norse leyðra "to clean, wash;" see lather (n.)). Related: Lathered; lathering.
Latin (adj.): Old English latin, from Latin Latinus "belonging to Latium," the region of Italy around Rome, possibly from PIE root *stela- "to spread, extend," with a sense of "flat country" (as opposed to the mountainous district of the Sabines), or from a prehistoric non-IE language. The Latin adjective also was used of the Roman language and people.
Centurion: What's this, then? ‘People called Romanes they go the house?’
Brian: It ... it says, ‘Romans, go home.’
Centurion [thrashing him like a schoolboy]: No, it doesn't. ‘Go home?' This is motion towards. Isn't it, boy?
Brian: Ah ... ah, dative, sir! Ahh! No, not dative! Not the dative, sir! No! Ah! Oh, the ... accusative! Domum, sir! Ah! Oooh! Ah!
Centurion [pulling him by the ear]: Except that domum takes the ...?
Brian: The locative, sir!
[Monty Python, "Life of Brian"]
Used as a designation for "people whose languages descend from Latin" (1856), hence Latin America (1862). The Latin Quarter (French Quartier latin) of Paris, on the south (left) bank of the Seine, was the site of university buildings in the Middle Ages, hence the place where Latin was spoken. The surname Latimer, Lattimore, etc. is from Vulgar Latin latimarus, from Latin latinarius "interpreter," literally "a speaker of Latin."
Latin (n.): "the language of the (ancient) Romans," Old English latin, from Latin latinium (see Latin (adj.)). The more common form in Old English was læden, from Vulgar Latin *ladinum, probably influenced by Old English leoden "language."
Latin America: 1862; see Latin (adj.). Related: Latin American (adj.), 1871.
Latino: "male Latin inhabitant of the United States" (fem. Latina), 1946, American English, from American Spanish, shortening of Latinoamericano "Latin-American" (see Latin America). As an adjective, attested from 1974.
Latino-: prefix in use from 1939; see Latino.
latitude (n.): late 14c., "breadth," from Old French latitude (13c.) and directly from Latin latitudo "breadth, width, extent, size," from latus "wide," from PIE root *stele- "to spread" (cf. Old Church Slavonic steljo "to spread out," Armenian lain "broad"). Geographical sense also is from late 14c., literally "breadth" of a map of the known world. Figurative sense of "allowable degree of variation" is early 15c. Related: Latitudinal.
latitudinarian (adj.): 1660s, "characterized by broad-mindedness," especially in reference to Episcopal clergymen indifferent to doctrinal details; from Latin latitudin-, from latitude in its meaning "freedom from narrow restrictions" (c.1600). Related: Latitudinarianism.
latke (n.): "pancake made with grated potatoes," 1927, from Yiddish, from Russian latka "pastry," said to mean literally "a patch," but by Watkins traced to Greek elaia "olive."
latrine (n.): c.1300, probably from Latin latrina, contraction of lavatrina "washbasin, washroom," from lavatus, past participle of lavare "to wash" (see lave) + -trina, suffix denoting "workplace." Its reappearance in 1640s is probably a re-borrowing from French; especially of a privy of a camp, barracks, college, hospital, etc. Latrine rumor "baseless gossip" (of the kind that spreads in conversations in latrines) is military slang, first recorded 1918.
latte (n.): by 1990, espresso coffee with milk, short for caffè latte, from Italian, literally "milk coffee" (see cafe au lait).
latter (adj.): Old English lætra "slower," comparative of læt "late" (see late (adj.)). Sense of "second of two" first recorded 1550s. The modern later is a formation from mid-15c.
latterly: 1734, from latter + -ly (2). Called by Johnson "a low word lately hatched." Related: Lattermost.
lattice (n.): c.1300, from Old French latiz "lattice," from late "lath, board, plank, batten" (Modern French latte), from Frankish or some other Germanic source, cf. Old High German latta "lath;" see lath).
latticework (n.): also lattice-work, late 15c., from lattice + work (n.).
Latvia: Baltic nation, independent from 1918, named for its inhabitants, Latvian Latvji, whose ancient name is of unknown origin. In English, the people name was Lett. Parts of the modern state were known previously as Livonia (from Estonian liiv "sand") and Courland (from Curonians, name of a Lettish people, of unknown origin).
laud (v.): late 14c., from Old French lauder "praise, extol," from Latin laudare "to praise, commend, honor, extol, eulogize," from laus (genitive laudis) "praise, fame glory." Probably cognate with Old English leoð "song, poem, hymn," from Proto-Germanic *leuthan (cf. Old Norse ljoð "strophe," German Lied "song," Gothic liuþon "to praise"), and from an echoic PIE root *leu-. Related: Lauded; lauding.
laudable (adj.): early 15c., from Old French laudable and directly from Latin laudabilis "praiseworthy," from laudare (see laud). Related: Laudably.
laudanum (n.): c.1600, from Modern Latin laudanum (1540s), coined by Paracelsus for a medicine he mixed, supposed to contain gold and crushed pearls and many expensive ingredients, but probably owing its effectiveness to only one of them, opium. Perhaps from Latin laudare "to praise," or from Latin ladanum "a gum resin," from Greek ladanon, a word perhaps of Semitic origin. The word soon came to be used for "any alcoholic tincture of opium." Latin ladanum was used in Middle English of plant resins, but this is not regarded as the source of the 16c. word.