lunatic (n.) Look up lunatic at Dictionary.com
"lunatic person," late 14c., from lunatic (adj.).
lunation (n.) Look up lunation at Dictionary.com
"time from one new moon to another," late 14c., from Medieval Latin lunationem, from luna "moon" (see Luna).
lunch (n.) Look up lunch at Dictionary.com
"mid-day repast," 1786, shortened form of luncheon (q.v.). The verb meaning "to take to lunch" (said to be from the noun) also is attested from 1786:
PRATTLE. I always to be ſure, makes a point to keep up the dignity of the family I lives in. Wou'd you take a more ſolid refreſhment?--Have you lunch'd, Mr. Bribe?

BRIBE. Lunch'd O dear! Permit me, my dear Mrs. Prattle, to refreſh my sponge, upon the honey dew that clings to your raviſhing pouters. O! Mrs. Prattle, this ſhall be my lunch. (kiſſes)

["The Mode," in William Davies' "Plays Written for a Private Theatre," London, 1786]
But as late as 1817 the only definition of lunch in Webster's is "a large piece of food." OED says in 1820s the word "was regarded either as a vulgarism, or as a fashionable affectation." Related: Lunched; lunching. Lunch money is attested from 1868; lunch-time (n.) is from 1821; lunch hour is from 1840. Slang phrase out to lunch "insane, stupid, clueless" first recorded 1955, on notion of being "not there." Old English had nonmete "afternoon meal," literally "noon-meat."
luncheon (n.) Look up luncheon at Dictionary.com
"light repast between mealtimes," 1650s (lunching; spelling luncheon by 1706); earlier "thick piece, hunk," 1570s (luncheon), of uncertain origin. Perhaps northern English dialectal lunch "hunk of bread or cheese" (1580s; probably from Spanish lonja "a slice," literally "loin"), blended with or influenced by nuncheon (Middle English nonechenche, mid-14c.) "light mid-day meal," from none "noon" (see noon) + schench "drink," from Old English scenc, from scencan "pour out."

Despite the form lunching in the 1650s source OED discounts that it possibly could be from lunch (v.), which is much later. It suggests perhaps an analogy with truncheon, etc. Especially in reference to an early afternoon meal eaten by those who have a noontime dinner.
luncheonette (n.) Look up luncheonette at Dictionary.com
type of restaurant, 1906, American English, from luncheon + diminutive ending -ette.
lune (n.) Look up lune at Dictionary.com
figure formed by two arcs of circles, 1704, from Latin luna "moon; crescent-shaped badge" (see luna).
lunette (n.) Look up lunette at Dictionary.com
1570s, "semi-circular horseshoe," from Middle French lunette (13c.), literally "little moon," diminutive of lune "moon," from Latin luna (see luna). Later applied to a wide range of objects and ornamentations resembling a crescent moon.
lung (n.) Look up lung at Dictionary.com
"human respiratory organ," c. 1300, from Old English lungen (plural), from Proto-Germanic *lungw- (cognates: Old Norse lunge, Old Frisian lungen, Middle Dutch longhe, Dutch long, Old High German lungun, German lunge "lung"), literally "the light organ," from PIE *legwh- "not heavy, having little weight; easy, agile, nimble" (cognates: Russian lëgkij, Polish lekki "light;" Russian lëgkoje "lung," Greek elaphros "light" in weight; see also lever).

The notion probably is from the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not. Compare also Portuguese leve "lung," from Latin levis "light;" Irish scaman "lungs," from scaman "light;" Welsh ysgyfaint "lungs," from ysgafn "light." See also lights, pulmonary. Lung cancer attested from 1882.
lunge (v.) Look up lunge at Dictionary.com
1735 (implied in lunged), from lunge (n.). Sense of "to make a sudden forward rush" is from 1821. Related: Lunged; lunging.
lunge (n.) Look up lunge at Dictionary.com
1735, "a thrust with a sword," originally a fencing term, shortened from allonge, from French allonger "to extend, thrust," from Old French alongier "to lengthen, make long," from à "to" + Old French long, from Latin longus "long" (see long (adj.)).
lungfish (n.) Look up lungfish at Dictionary.com
1883, from lung + fish (n.).
lunk (n.) Look up lunk at Dictionary.com
"slow-witted person," 1867, American English colloquial, shortened from lunkhead (1852), possibly an altered form of lump (n.) + head (n.)
Lupercalia (n.) Look up Lupercalia at Dictionary.com
Roman festival held Feb. 15, in honor of Lupercus, god (identified with Lycean Pan) who had a grotto at the foot of the Palatine Hill, from Latin Lupercalia (plural), from Lupercalis "pertaining to Lupercus," whose name derives from lupus "wolf" (see wolf (n.)).
lupin (n.) Look up lupin at Dictionary.com
plant of the genus lupinus, late 14c., from Latin lupinus, name of the plant, noun use of an adjective meaning "of a wolf" (see lupine). The reason for association with the animal is unclear; perhaps it was so called because of a belief that the plants were harmful to soil (compare lupus).
lupine (adj.) Look up lupine at Dictionary.com
"wolf-like," 1650s, from French lupine "wolf-like," from Latin lupinus "of the wolf," from lupus "wolf" (see wolf (n.)).
lupus (n.) Look up lupus at Dictionary.com
late 14c., used of several diseases that cause ulcerations of the skin, from Medieval Latin lupus, from Latin lupus "wolf" (see wolf (n.)), apparently because it "devours" the affected part.
lurch (n.1) Look up lurch at Dictionary.com
"sudden pitch to one side," 1784, from earlier lee-larches (1765), a nautical term for "the sudden roll which a ship makes to lee-ward in a high sea, when a large wave strikes her, and bears her weather-side violently up, which depresses the other in proportion" ["Complete Dictionary of Arts and Sciences," London 1765]; perhaps from French lacher "to let go," from Latin laxus (see lax).
When a Ship is brought by the Lee, it is commonly occaſsioned by a large Sea, and by the Neglect of the Helm's-man. When the Wind is two or three Points on the Quarter, the Ship taking a Lurch, brings the Wind on the other Side, and lays the Sails all dead to the Maſt; as the Yards are braced up, ſhe then having no Way, and the Helm being of no Service, I would therefore brace about the Head ſails ſharp the other Way .... [John Hamilton Moore, Practical Navigator, 8th ed., 1784]
lurch (n.2) Look up lurch at Dictionary.com
"predicament," 1580s, from Middle English lurch (v.) "to beat in a game of skill (often by a great many points)," mid-14c., probably literally "to make a complete victory in lorche," a game akin to backgammon, from Old French lourche. The game name is perhaps related to Middle English lurken, lorken "to lie hidden, lie in ambush," or it may be adopted into French from Middle High German lurz "left," also "wrong."
lurch (v.) Look up lurch at Dictionary.com
1821, from lurch (n.1). Related: Lurched; lurching.
lure (v.) Look up lure at Dictionary.com
late 14c., of hawks, also of persons, from lure (n.). Related: Lured; luring.
lure (n.) Look up lure at Dictionary.com
early 14c., "something which allures or entices, an attraction" (a figurative use), also "bait for recalling hawks," from Anglo-French lure, Old French loirre "device used to recall hawks, lure," from Frankish *loþr or some other Germanic source, from Proto-Germanic *lothran "to call" (cognates: Middle High German luoder, Middle Low German loder "lure, bait," German Luder "lure, deceit, bait;" also Old English laþian "to call, invite," German laden).

Originally a bunch of feathers on a long cord, from which the hawk is fed during its training. Used of means of alluring other animals (especially fish) from c. 1700. Technically, bait is something the animal can eat; lure is a more general term. Also in 15c. a collective word for a group of young women.
lurid (adj.) Look up lurid at Dictionary.com
1650s, "pale," from Latin luridus "pale yellow, ghastly," of uncertain origin, perhaps cognate with Greek khloros (see Chloe). Meaning "glowing in the darkness" is from 1727. The figurative sense of "sensational" is first attested 1850. Related: Luridly.
lurk (v.) Look up lurk at Dictionary.com
c. 1300, lurken "to hide, lie hidden," probably from Scandinavian (compare dialectal Norwegian lurka "to sneak away," dialectal Swedish lurka "to be slow in one's work"), perhaps ultimately related to Middle English luren "to frown, lurk" (see lower (v.2)). Related: Lurked; lurking.
lurker (n.) Look up lurker at Dictionary.com
"one who lurks," early 14c., agent noun from lurk (v.).
luscious (adj.) Look up luscious at Dictionary.com
late 15c., perhaps a variant (with form perhaps influenced by Old French luxure, lusure) of Middle English licius "delicious" (c. 1400), which is perhaps a shortening of delicious, but OED is against this. Related: Lusciously; lusciousness.
lush (adj.) Look up lush at Dictionary.com
mid-15c., "lax, flaccid, soft, tender," from Old French lasche "soft, succulent," from laschier "loosen," from Late Latin laxicare "become shaky," related to Latin laxare "loosen," from laxus "loose" (see lax). Sense of "luxuriant in growth" is first attested c. 1600, in Shakespeare. Applied to colors since 1744. Related: Lushly; lushness.
lush (n.) Look up lush at Dictionary.com
"drunkard," 1890, from earlier (1790) slang meaning "liquor" (especially in phrase lush ken "alehouse"); perhaps a humorous use of lush (adj.) or from Romany or Shelta (tinkers' jargon).
LUSHEY. Drunk. The rolling kiddeys had a spree, and got bloody lushey; the dashing lads went on a party of pleasure, and got very drunk. ["Dictionary of Buckish Slang, University Wit, and Pickpocket Eloquence," London, 1811]
Lusitania Look up Lusitania at Dictionary.com
Latin name of a region roughly corresponding to modern Portugal; in modern use, allusive or poetic for "Portugal." The Cunard ocean liner (sister ship of the Mauretania and Aquitania, also named after Roman Atlantic coastal provinces) was launched in 1906, torpedoed and sunk by German submarine U-20 on May 7, 1915.
lusory (adj.) Look up lusory at Dictionary.com
1650s, from Latin lusorius "belonging to a player," from lusor "player," from stem of ludere "to play" (see ludicrous). Related: Lusorious.
lust (v.) Look up lust at Dictionary.com
c. 1200, "to wish, to desire," from lust (n.) and Old English lystan (see list (v.4)). Sense of "to have a strong sexual desire (for or after)" is first attested 1520s in biblical use. Related: Lusted; lusting.
lust (n.) Look up lust at Dictionary.com
Old English lust "desire, appetite, pleasure; sensuous appetite," from Proto-Germanic *lustuz (cognates: Old Saxon, Old Frisian, Dutch, German lust, Old Norse lyst, Gothic lustus "pleasure, desire, lust"), from PIE *las- "to be eager, wanton, or unruly" (cognates: Latin lascivus "wanton, playful, lustful;" see lascivious).

In Middle English, "any source of pleasure or delight," also "an appetite," also "a liking for a person," also "fertility" (of soil). Sense of "sinful sexual desire, degrading animal passion" (now the main meaning) developed in late Old English from the word's use in Bible translations (such as lusts of the flesh to render Latin concupiscentia carnis [I John ii:16]); the cognate words in other Germanic languages tend still to mean simply "pleasure."
luster (n.1) Look up luster at Dictionary.com
"gloss, radiance," 1520s, from Middle French lustre "gloss, radiance" (14c.), common Romanic (cognates: Spanish and Portuguese lustre, Rumanian lustru, Italian lustro "splendor, brilliancy"), from Latin lustrare "spread light over, brighten, illumine," related to lucere "shine," lux "light" (see light (n.)).
luster (n.2) Look up luster at Dictionary.com
"one who lusts," 1590s, agent noun from lust (v.).
lustful (adj.) Look up lustful at Dictionary.com
Old English lustfull "wishful, desirous, having an eager desire;" see lust (n.) + -ful. Specifically of sexual desire from 1570s. Related: Lustfully; lustfulness. Middle English also had lustsome, which was used in a sense of "voluptuous, lustful" from c. 1400. Old English had lustbære "desirable, pleasant, cheerful, joyous."
lustgarden (n.) Look up lustgarden at Dictionary.com
1580s, translation or partial translation of German Lust-garten, Dutch lustgaard "pleasure garden;" see lust (n.) + garden (n.).
lustily (adv.) Look up lustily at Dictionary.com
early 13c., lustliche, "willingly, eagerly, readily;" see lusty + -ly (2). Meaning "with pleasure, voluptuously" is c. 1300; meaning "vigorously, energetically" is c. 1400.
lustral (adj.) Look up lustral at Dictionary.com
"pertaining to purification," 1530s, from Latin lustralis, from lustrum (see lustrum). Hence, also, "every five years" (1781).
lustre (n.) Look up lustre at Dictionary.com
"gloss, radiance;" see luster (n.1).
lustrous Look up lustrous at Dictionary.com
c. 1600, from luster + -ous. Related: Lustrously; lustrousness.
lustrum (n.) Look up lustrum at Dictionary.com
(plural lustra), "purification of the Roman people every five years," 1580s, from Latin lustrum, perhaps from root of luere "to wash," related to lavere (see lave). Or [Watkins, Klein] from PIE *leuk-stro-, from base *leuk- "light, brightness."
lusty (adj.) Look up lusty at Dictionary.com
early 13c., "joyful, merry," from lust + -y (2). It largely has escaped the Christianization and denigration of its root word. The sense of "full of healthy vigor" is from late 14c.; that of "full of desire" is attested from c. 1400. Related: Lustily; lustiness.
lute (n.) Look up lute at Dictionary.com
stringed musical instrument, late 13c., from Old French lut, leut, from Old Provençal laut, from Arabic al-'ud, the Arabian lute, literally "the wood" (source of Spanish laud, Portuguese alaude, Italian liuto), where al is the definite article. A player is a lutist (1620s) or a lutanist (c. 1600, from Medieval Latin hybrid lutanista).
luteal (adj.) Look up luteal at Dictionary.com
"pertaining to the corpus luteum," 1906, from Latin luteus "yellow" (see luteous). Luteal phase is attested by 1932.
luteous (adj.) Look up luteous at Dictionary.com
"orange-yellow," 1650s, from Latin luteus "golden-yellow, orange-yellow," from lutum, the name of a plant used in dying yellow, of unknown origin.
Lutheran Look up Lutheran at Dictionary.com
1521, from name of German religious reformer Martin Luther (1483-1546); used by Catholics 16c. in reference to all Protestants, regardless of sect. Related: Lutheranism.
luthier (n.) Look up luthier at Dictionary.com
"lute-maker," 1879, from French luthier, from luth (see lute).
lutz (n.) Look up lutz at Dictionary.com
type of skating jump, 1932, from the name Alois Lutz, "an obscure Austrian skater of the 1920s" [James R. Hines, "Historical Dictionary of Figure Skating," 2011], who is said to have first performed it in 1913.
luv Look up luv at Dictionary.com
affectionate, dialectal, or colloquial spelling of love, attested from 1825.
lux (n.) Look up lux at Dictionary.com
unit of illumination, 1889, from Latin lux "light" (see light (n.)).
luxe Look up luxe at Dictionary.com
"luxury, elegance," 1550s, from French luxe "luxury, sumptuousness, profusion," from Latin luxus (see luxury).