ludic (adj.)
"spontaneously playful," 1940, a term in psychiatry, from French ludique, from Latin ludere "to play" (see ludicrous).
ludicrous (adj.)
1610s, "pertaining to play or sport" (a sense now obsolete), from Latin ludicrus "sportive" (source of Old French ludicre), from ludicrum "amusement, game, toy, source of amusement, joke," from ludere "to play."

This verb, along with Latin ludus "a game, play," is from the PIE root *leid- or *loid- "to play," perhaps literally "to let go frequently" [de Vaan], which is the source also of Middle Irish laidid "impels;" Greek lindesthai "to contend," lizei "plays;" Albanian lind "gives birth," lindet "is born;" Old Lithuanian ledimi "I let," Lithuanian leisti "to let," laidyti "to throw," Latvian laist "let, publish, set in motion."

Sense of "ridiculous, apt to evoke ridicule or jest" is attested from 1782. Related: Ludicrously; ludicrousness.
masc. proper name, from Old High German hlud(o)wig, literally "famous in war," from Proto-Germanic *hluda- "heard of, famous" (see loud) + *wiga "war" (see victory). Compare Louis.
luff (n.)
also loof, in sailing, c. 1200, "contrivance for altering a ship's course," also "part of a ship's bow where the sides begin to curve," from Old French lof "spar," or some other nautical device, "point of sail," also "windward side," of uncertain origin and sense development, probably ultimately from Germanic (compare Middle Dutch lof "windward side of a ship" (Dutch loef), which might also be the direct source of the English word).

This is from Proto-Germanic *lofo (source also of Old Norse lofi, Gothic lofa "palm of the hand," Danish lab, Swedish labb "paw"), from PIE *lep- (2) "to be flat" (see glove (n.)). As a verb, "bring the head of a sailing-ship nearer the wind," from late 14c., from the noun.
air arm of the German Wehrmacht in the World War II era, 1935, from German Luftwaffe, literally "air-weapon," from Luft (see loft (n.)) + Waffe (see weapon (n.)).
lug (v.)
late 14c., "pull (something) slowly or with effort," from Scandinavian (compare Swedish lugga, Norwegian lugge "to pull by the hair"); see lug (n.). Related: Lugged; lugging.
lug (n.)
a broad-meaning word used of things that move slowly or with difficulty, "of obscure etymology" [OED]. From 1620s as "handle of a pitcher," this sense probably from Scottish lugge "earflap of a cap; ear" (late 15c. and according to OED still the common word for "ear" in 19c. Scotland), which is probably from Scandinavian (compare Swedish lugg "forelock," Norwegian lugg "tuft of hair") and influenced by the verb. The connecting notion is "something that can be gripped and pulled." Applied 19c. to mechanical objects that can be grabbed or gripped. Meaning "stupid fellow" is from 1924; that of "lout, sponger" is 1931, American English. Compare lug-nut (1869), nut closed at one end as a cap.
lug-sail (n.)
1670s, probably from lug (n.) in some obscure sense; perhaps so called from the "ear" of sail formed by the oblique hang of the yard from the mast.
lug-worm (n.)
type of large worm inhabiting muddy and sandy soil along seashores, also lugworm, 1802, with worm (n.) + lug, which by itself was the older name for the worm (c. 1600). This is perhaps from lug, noun or verb (on the notion of "heavy, clumsy"), or perhaps it is from a Celtic word (the first recorded use is in a Cornwall context).
Bantu language spoken in Uganda, from Ganda, indigenous people name, which is of unknown origin.
luge (n.)
kind of small toboggan, 1905, from French luge "small coasting sled," from Savoy dialect, from Medieval Latin sludia "sled" (9c.), which is perhaps from a Gaulish word from the same root as English sled, slide.
Luger (n.)
type of German automatic pistol, 1904, from the surname of Georg Luger (1849-1923), Austrian-born firearms expert.
luggage (n.)
1590s, from lug (v.) "to drag" + -age; so, literally "what has to be lugged about" (or, in Johnson's definition, "any thing of more weight than value"). In 20c., the usual British word for "baggage belonging to passengers."
lugger (n.)
"small two- or three-masted fishing or coasting boat" (also favored by smugglers), always with lug-sails, 1757, from lug-sail. Or else [OED] from Dutch logger, which is perhaps from Middle Dutch loggen "to fish with a dragnet."
lugubriosity (n.)
1839, abstract noun from lugubrious. Sometimes also lugubrosity.
lugubrious (adj.)
c. 1600, formerly also lugubrous, from -ous + Latin lugubris "mournful, doleful, pertaining to mourning," from lugere "to mourn," from PIE root *leug- "to break; to cause pain" (source also of Greek lygros "mournful, sad," Sanskrit rujati "breaks, torments," Lettish lauzit "to break the heart"). Related: Lugubriously; lugubriousness.
luke (adj.)
obsolete except in lukewarm (late 14c.), from Middle English leuk "tepid" (c. 1200), a word of uncertain origin, perhaps from an unrecorded Old English *hleoc (cognate with Middle Dutch or Old Frisian leuk "tepid, weak"), an unexplained variant of hleowe (adv.) "warm," from Proto-Germanic *khlewaz (see lee). Old English also had wlæc "tepid, lukewarm," which survived in Middle English as wlake. In Middle English lew-warm was a parallel form to luke-warm. Related: Lukely; lukeness. Other now-obsolete formations were luke-hot (late 14c.), luke-hearted (c. 1500).
masc. proper name, from Latin Lucas (Greek Loukas), contraction of Lucanus literally "of Lucania," district in Lower Italy, home of the Lucani, a branch of the Sabelline race. St. Luke, the Evangelist, is believed by some scholars to have been a Greek or Hellenized Jewish physician of Antioch. His feast day (Oct. 18) was formerly Lukesmas.
lukewarm (adj.)
"neither cold nor hot, tepid," late 14c., from warm (adj.) + luke (adj.) "tepid" (c. 1200), a word of unknown origin. Perhaps it is from Middle Dutch or Old Frisian leuk "tepid, weak," or an unexplained variant of Old English hleowe (adv.) "warm," all of which are from Proto-Germanic *khlewaz (from PIE root *kele- (1) "warm;" compare lee).

Figurative sense of "lacking in zeal, not ardent" (of persons or their actions) is from 1520s. Related: Lukewarmly; lukewarmness. Luke-warmth (1590s) is marked "rare" in OED.
lull (n.)
1650s as the name of a soothing drink, from lull (v.). Meaning "temporary period of quiet or rest amid turmoil or activity" is from 1815.
lull (v.)
early 14c., lullen "to calm or hush to sleep," probably imitative of lu-lu sound used to lull a child to sleep (compare Swedish lulla "to hum a lullaby," German lullen "to rock," Sanskrit lolati "moves to and fro," Middle Dutch lollen "to mutter"). Figurative use from 1570s; specifically "to quiet (suspicion) so as to delude into a sense of security" is from c. 1600. Related: Lulled; lulling.
lullaby (n.)
"soothing song sung to infants," 1580s, noun use of the words lulley by (1560s), from Middle English lollai or lullay, a common burden in nursery songs, from lullen (see lull (v.)). Second element perhaps from by in good-bye or simply a meaningless extension.
lulu (n.)
"remarkable person or thing," 1886, of uncertain origin but likely a reference to Lulu Hurst (1869-1950), the "Georgia Wonder," who was a popular attraction 1883-85 demonstrating her supposed mysterious "force" that allowed her to effortlessly move, with just a light touch, umbrellas and canes held tight by others. She barnstormed the U.S. and, at 15, was, briefly, one of the most famous women in the land. The skeptics soon explained her trick and burst the bubble, but not before her name was used as a word:
Such [musically uneducated persons] start from the avowed or unavowed supposition that the pianist or violinist's art necessitates no higher qualities than does plate-spinning, dancing, or the feats of a Lulu. ["The Hero as Virtuoso," in "London Society," vol. 43, June 1883]
lumbaginous (adj.)
"afflicted with lumbago," 1610s, from Latin combining form of lumbago + -ous.
lumbago (n.)
1690s, from Late Latin lumbago "weakness of loins and lower back," from Latin lumbus "hip, loin" (usually plural), from Proto-Italic *londwo- "loins," from PIE *lendh- (1) "loin" (see lumbo-).
lumbar (adj.)
"pertaining to or situated near the loins," 1650s, from Modern Latin lumbaris, from Latin lumbus "loin" (see lumbo-).
lumber (v.1)
"to move clumsily," c. 1300, lomere, probably from a Scandinavian source (compare dialectal Swedish loma "move slowly, walk heavily," Old Norse lami "lame"), which is perhaps from PIE root *lem- "break in pieces," with derivatives meaning "crippled," and ultimately cognate with lame (adj.). "Possibly two or more words may have coalesced" [OED]. With unetymological -b- as in humble, nimble, etc. Related: Lumbered; lumbering; lumbersome.
lumber (v.2)
"cut forest trees," 1809, American English, from lumber (n.). Related: Lumbered; lumbering.
lumber (n.)
"timber sawn into rough planks for use," 1660s, American English (Massachusetts), earlier "disused bit of furniture; heavy, useless objects" (1550s), of uncertain origin. It is said to be probably from lumber (v.1) on the notion of "awkward to move," and perhaps to have been influenced by or associated with Lombard (q.v.), the Italian immigrant class famous as pawnbrokers (and money-lenders) in old England. Lumbar and Lumbard were old alternative forms of Lombard in English.

The evolution of sense then would be because a lumber-house ("pawn shop; place where thieves stash stolen property") naturally accumulates odds and ends of furniture. The 19th century guess was that it comes directly from lumber-house or lumber-room in the pawn shop sense, but these are not attested before lumber (n.). Lumber camp is from 1882; lumber-mill is from 1830; lumber-yard is from 1786.
Live Lumber, soldiers or passengers on board a ship are so called by the sailors. [Grose, "Dictionary of the Vulgar Tongue," 1785]
lumberjack (n.)
1831, Canadian English, from lumber (n.) + jack (n.) "man, fellow." Lumberman in the same sense is from 1817.
word-forming element used since 19c. and meaning "loin, loins," from Latin lumbus "hip, loin" (usually plural), from Proto-Italic *londwo- "loins," from PIE *lendh- (1) "loin" (source also of Sanskrit randhra- "loin (of animals);" Old Church Slavonic ledvije (plural) "loins, kidneys, insides; soul," Russian ljadveja (archaic) "thigh;" Old English lendenu "loins," Old Norse lend, German Lende "loin," Lenden "loins").
lumen (n.)
unit of luminosity, 1897, coined in French 1894 by French physicist André-Eugène Blondel (1863-1938) from Latin lumen "light" (n.), from suffixed form of PIE root *leuk- "light, brightness." Earlier it was used in anatomy for "an opening or passageway" (1873).
Lumiere (adj.)
in reference to the early color photography process, from the names of French brothers Auguste (1862-1954) and Louis (1864-1948) Lumière, photographers who pioneered the movie camera. The name is literally "light, lamp."
luminaire (n.)
electric lighting unit, 1921, a trade term, from French luminaire, from Old French luminarie "lamp, candle; brightness, illumination" (see luminary).
luminal (adj.)
1897, "of or pertaining to a lumen," with -al (1).
Luminal (n.)
trade name of phenobarbitone, used as a sedative and hypnotic, coined 1912 in German from Latin lumen "light" (from suffixed form of PIE root *leuk- "light, brightness") + -al (3), "the root here being used, very irregularly, as an equivalent of pheno-" [Flood].
luminance (n.)
"luminousness," 1862, from Late Latin luminantem (nominative luminans), present participle of luminare "to shine," from Latin lumen (genitive luminis) "light," from suffixed form of PIE root *leuk- "light, brightness." Related: Luminant.
luminary (n.)
mid-15c., "lamp, light-giver, source of light," from Old French luminarie (12c.), "lamp, lights, lighting; candles; brightness, illumination," from Late Latin luminare "light, torch, lamp, heavenly body," literally "that which gives light," from Latin lumen (genitive luminis) "light, source of light, daylight, the light of the eye; distinguished person, ornament, glory," related to lucere "to shine," from suffixed (iterative) form of PIE root *leuk- "light, brightness."

From late 15c. as "celestial body." Sense of "notable person" is first recorded 1690s, though the Middle English word also had a figurative sense of "source of spiritual light, example of holiness" (mid-15c.). As an adjective, "pertaining to light," from 1794 but this is rare.
luminate (v.)
"to light up, illuminate," 1620s (obsolete), from *luminatus, past participle of Late Latin luminare "to shine," from Latin lumen (genitive luminis) "light," from suffixed form of PIE root *leuk- "light, brightness." Illuminate now does the job. An older verb was lumine (late 14c.); a newer one is luminize (1958). Related: Luminated; luminating; lumination; luminator.
luminescence (n.)
1884, coined in German physicist Eilhard Wiedemann (1852-1928) from Latin lumen (genitive luminis) "light" (from suffixed form of PIE root *leuk- "light, brightness") + -escence.
Fluorescence and Phosphorescence -- Prof. E. Wiedmann has made a new study of these phenomena. He proposes the general name luminescence for evolutions of light which do not depend on the temperature of the substance concerned. ["Photographic News," April 20, 1888]
The verb luminesce (1896) is a back-formation.
luminescent (adj.)
"characterized by luminescence," 1889; see luminescence + -ent.
luminosity (n.)
1630s, "quality of being luminous," from French luminosité (cognate with Medieval Latin luminositas "splendor") or else a native formation from luminous + -ity. Meaning "intensity of light in a color" (of a flame, spectrum, etc.) is from 1876. In astronomy, "intrinsic brightness of a heavenly body" (as distinguished from apparent magnitude, which diminishes with distance), attested from 1906.
luminous (adj.)
early 15c., "full of light, shiny," from Latin luminosus "shining, full of light, conspicuous," from lumen (genitive luminis) "light," from suffixed form of PIE root *leuk- "light, brightness." Related: Luminously; luminousness.
lummox (n.)
"clumsy, stupid man," 1825, East Anglian slang, of unknown origin. Perhaps from dumb ox, influenced by lumbering; or from or related to dialectal verb lummock "move heavily or clumsily," itself a word of uncertain origin.
lump (v.1)
early 15c., "to curl up in a ball, to gather into a lump" (implied in lumped), from lump (n.). Transitive meaning "to put together in one mass or group" is from 1620s. Related: Lumped; lumping (from 1705 as a slang present-participle adjective meaning "great, big"):
LUMPING. Great. A lumping pennyworth; a great quantity for the money, a bargain. He has got a lumping pennyworth; frequently said of a man who marries a fat woman. [Grose, "Classical Dictionary of the Vulgar Tongue," 3rd edition, 1796]
lump (n.)
early 14c., lumpe, "small mass of material, solid but of irregular shape" (1224 as surname), etymology and original sense unknown. Perhaps it was in Old English, but it is not recorded there. Perhaps from a Scandinavian or continental source: Compare Danish lumpe "block, stump, log" (16c.), Middle High German lumpe, early modern Dutch lompe. All appear in the Middle Ages; there seems to be no trace of the word in older Germanic languages.

Late 15c. as "protuberant part;" from 1520s as "a great quantity;" 1590s as "dull, stupid person." Phrase lump in (one's) throat "swelling in the throat," especially "feeling of tightness brought on by emotion," is from 1803. Lumps "hard knocks, a beating" is colloquial, from 1934. Lump sum, covering a number of items at one time, is from 1867 (the same sense of lump is in lump-work, 1851).
lump (v.2)
"endure" (now usually in antithesis to like), 1791, apparently an extended sense from an older meaning "to look sulky, dislike" (1570s), of unknown origin, perhaps, as OED suggests "of symbolic sound" (compare grump, harumph, glum, etc.). Or from lump (n.) on the notion of "swallow the whole."
lumpectomy (n.)
1971, from lump (n.) on model of mastectomy.
lumpenproletariat (n.)
1897, from German Lumpenproletariat (1850), from Marx, who coined it and used it to mean "the rabble, poorest of the working class," "who make no contribution to the workers' cause" [OED]. From German lump "ragamuffin," which is related to lumpen "a rag, tatter," probably ultimately related to English lump (n.). With proletariat. Its secondary sense of "boorish, stupid people" led to lumpen- being taken as a suffix meaning "unenlightened."
lumpish (adj.)
1520s, from lump (n.) + -ish.