Online Etymology Dictionary

lustily (adv.): early 13c., lustliche, "willingly, eagerly, readily;" see lusty + -ly (2). Meaning "with pleasure, voluptuously" is c. 1300; meaning "vigorously, energetically" is c. 1400. Sometimes 15c.-16c. with a sense "lustfully, carnally," but this now goes with lustfully.
lustless (adj.): early 14c., "wanting vigor or energy," from lust (n.) + -less. From 1580s as "wanting sexual appetite."
lustral (adj.): "pertaining to purification," 1530s, from Latin lustralis "of purification," from lustrum "purification; ritual purification of the Roman people every five years" (see lustrum). Hence, also, "every five years" (1781).
lustrate (v.): "purify by means of an offering," 1650s, from Latin lustratus, past participle of lustrare "purify ceremonially," from lustrum "purificatory sacrifice" (see lustrum) Related: Lustration (1610s).
lustre (n.): "gloss, radiance," 1520s, from French lustre (see luster (n.1), and see -re. Related: Lustreless.
lustrous: c. 1600, "reflecting light;" 1742 "giving or shedding light;" see luster (n.1) + -ous. Related: Lustrously; lustrousness.
lustrum (n.): (plural lustra), "ceremonial purification of the Roman people every five years," 1580s, from Latin lustrum "a purificatory sacrifice, ceremony of purification; five-year period," from Proto-Italic *lustro- "expiation," which is of uncertain origin. Perhaps [OED] from root of luere "to wash" (from PIE root *leue- "to wash"). Or [Watkins, Klein], based on a possible earlier meaning "illumination," from PIE *leuk-stro-, from root *leuk- "light, brightness." De Vaan prefers as most likely the explanation "that lustrum was derived from *luH- 'to set free'," with suffix *-stro- also found in monstrum, etc.
lusty (adj.): early 13c., "joyful, merry;" late 14c., "full of healthy vigor," from lust (n.) + -y (2). Used of handsome dress, fine weather, good food, pleasing language, it largely escaped the Christianization and denigration of the noun in English. The sense of "full of desire" is attested from c. 1400 but seems to have remained secondary. Related: Lustily; lustiness.
lusus naturae (n.): in natural history, "freak of nature," 1660s, a Latin phrase, from lusus "a play," from stem of ludere "to play" (see ludicrous) + genitive of natura (see nature (n.)). Originally of fossils, before there was a scientific basis for understanding their existence.
lute (n.): stringed musical instrument, late 13c., from Old French lut, leut (Modern French luth), from Old Provençal laut, a misdivision of Arabic al-'ud, the Arabian lute, literally "the wood" (source of Medieval Latin lutana, Spanish laud, Portuguese alaude, Italian liuto), where al is the definite article.

Dutch luit, German Laute, Danish luth are from Romanic. A player is a luter (Middle English), a lutist (1620s) or a lutanist (c. 1600, from Medieval Latin lutanista).
lute-string (n.): 1520s, from lute (n.) + string (n.).
luteal (adj.): "pertaining to the corpus luteum," 1906, from Latin luteus "yellow," from lutum, the name of a weed used in dying yellow, a word of unknown origin. Luteal phase is attested by 1932.
luteous (adj.): "deep orange-yellowish," 1650s, from Latin luteus "golden-yellow, orange-yellow," from lutum, the name of a weed used in dying yellow, a word of unknown origin.
Lutetian (adj.): archaic or humorous way to say "Parisian," from the old Gallo-Roman name of the place, Lutetia Parisorum (see Paris), literally "Parisian swamps," from Latin lutum "mud, dirt, clay" (see lutose).
lutetium (n.): rare metallic element, 1907, from French lutécium, from Latin Lutetia, representing "Paris" (see Paris) + metallic element ending -ium.
Lutheran: 1520s, adjective and noun, "of or pertaining to Martin Luther or to the sect he founded, which has his name, or its doctrines," from name of German religious reformer Martin Luther (1483-1546). Luther called it the Evangelical Church. Used by Catholics 16c. in reference to all Protestants, regardless of sect. In 16c. Lutherian also was used. Related: Lutheranism (1560s).
luthier (n.): "lute-maker," 1879, from French luthier, from luth (see lute).
lutose (adj.): "muddy, covered with clay," from Latin lutosus, from lutum "mud, dirt, mire, clay," from Proto-Italic *luto-, *lustro-, from PIE *l(h)u-to- "dirt," *l(h)u-(s)tro- "dirty place," from root *leu- "dirt; make dirty" (cognates: Greek lythron "gore, clotted blood," lyma "dirty water; moral filth, disgrace," lymax "rubbish, refuse," lyme "maltreatment, damage;" Latin lues "filth;" Old Irish loth "mud, dirt;" Welsh lludedic "muddy, slimy; Albanian lum "slime, mud;" Lithuanian liutynas "loam pit").

Hence also English lute (n.) as a type of tenacious clay or cement used to stop holes, seal joints, etc. (c. 1400), from Old French lut or Medieval Latin lutum, from the Latin noun. Lute also was a verb in English.
lutz (n.): 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. The surname is from a form of Ludwig.
luv: affectionate, dialectal, or colloquial spelling of love (noun and verb), attested from 1825.
Luvian (n.): 1924, language of an ancient Anatolian people contemporary with the Hittites, from an old name for that region of Asia Minor.
lux (n.): unit of illumination, 1889, from Latin lux "light," from PIE root *leuk- "light, brightness."
luxate (v.): "dislocate," 1590s, from Latin luxatus, past participle of luxare "dislocate," literally "oblique" (see luxation).
luxation (n.): "dislocation of a bone or joint," 1550s, from Late Latin luxationem (nominative luxatio) "a dislocation," noun of action from past participle stem of Latin luxare "dislocate," literally "oblique," from Greek loxos "bent to the side, slanting, oblique," figuratively "ambiguous," a word of uncertain origin.
luxe: "luxury, elegance," 1550s, from French luxe "luxury, sumptuousness, profusion," from Latin luxus (see luxury).
Luxembourg: European state, from Germanic lutilla "little" + burg "fort, castle." Related: Luxembourgeois (1905); Luxembourger (1913). Hence also lushburg (mid-14c.), Middle English word for "a base coin made in imitation of the sterling or silver penny and imported from Luxemburg in the reign of Edward III" [OED].
Luxor: place in Egypt, from a misdivision of Arabic al-uqsur, plural of al-qasr, which is from an Arabicized form of Latin castrum "fortified camp" (see castle (n.)). Remains of Roman camps are nearby.
luxuriance (n.): "abundant or vigorous growth or quantity," 1650s; see luxuriant + -ance. Related: Luxuriancy (1640s).
luxuriant (adj.): "exuberant in growth or quantity," 1530s, from Middle French luxuriant and directly from Latin luxuriantem (nominative luxurians), present participle of luxuriare "have to excess, grow profusely" (see luxuriate). Related: Luxuriantly.
luxuriate (v.): 1620s, "grow exuberantly or in abundance," also "indulge in luxury," from Latin luxuriatus, past participle of luxuriare "have to excess," figuratively "run riot, be dissolute, indulge to excess," from luxuria "excess, rankness, luxuriance" (see luxury). Related: Luxuriated; luxuriating.
luxurious (adj.): c. 1300, "lascivious, lecherous, unchaste," from Old French luxurios "lustful, lascivious" (Modern French luxurieux), from Latin luxuriosus "immoderate, excessive; voluptuous; profuse," from luxuria "excess, profusion; extravagant living" (see luxury). Meaning "given to luxury, voluptuous" (of persons) is from c. 1600. Of things, "characterized by luxury," from 1640s. Related: Luxuriously; luxuriousness.
luxury (n.): c. 1300, "sexual intercourse;" mid-14c., "lasciviousness, sinful self-indulgence;" late 14c., "sensual pleasure," from Old French luxurie "debauchery, dissoluteness, lust" (12c., Modern French luxure), from Latin luxuria "excess, extravagant living, profusion; delicacy" (source also of Spanish lujuria, Italian lussuria), from luxus "excess, extravagance; magnificence," probably a figurative use of luxus (adj.) "dislocated," which is related to luctari "wrestle, strain" (see reluctance).

The English word lost its pejorative taint 17c. Meaning "habit of indulgence in what is choice or costly" is from 1630s; that of "sumptuous surroundings" is from 1704; that of "something choice or comfortable beyond life's necessities" is from 1780. Used as an adjective from 1916.
In Lat. and in the Rom. langs. the word connotes vicious indulgence, the neutral sense of the Eng. 'luxury' being expressed by L. luxus, F. luxe, Sp. lujo, It. lusso. [OED]
LXX (n.): Roman numerals for "seventy," hence "the Septuagint" (q.v.).
lycanthrope (n.): 1620s in the classical sense "one who imagines himself to be a wolf and behaves as one;" 1825 in the modern sense "werewolf, human who supernaturally transforms into a wolf," from Modern Latin lycanthropus, from Greek lykanthropos "wolf-man" (see lycanthropy), and compare werewolf. Related: Lycanthropic.
lycanthropy (n.): 1580s, a form of madness (described by ancient writers) in which the afflicted thought he was a wolf, from Greek lykanthropia, from lykanthropos "wolf-man," from lykos "wolf" (see wolf (n.)) + anthropos "man" (from PIE root *ner- (2) "man"). Applied to actual transformations of persons (especially witches) into wolves since 1830 (see werewolf).
Lycaonian (adj.): in reference to an ancient region in Asia Minor, from Latin Lycaonia, from Greek Lykaonia,
lyceum (n.): 1580s, Latin form of Greek lykeion, name of a grove or garden with covered walks in the eastern suburb of ancient Athens, also the site of an athletic facility. Aristotle taught there. The name is from the neuter of Lykeios, an epithet of Apollo under which he had a temple nearby, which probably meant or was understood to mean "wolfish" (the exact legend appears to have become muddled), from lykos "wolf" (see wolf (n.)). Frazer (Pausanias) notes "The same epithet was applied to Apollo at Sicyon and Argos," and adds that "Wolves were dear to Apollo ... and they frequently appear in the myths told of him," and lists several.
But what gives the Lyceum its chief interest is that here, pacing the shady walks of the gymnasium, Aristotle expounded to his disciples that philosophy which was destined to influence so profoundly the course of European thought for two thousand years. [Frazer, "Pausanias's Description of Greece"]
Hence lycée, name given in France to secondary schools maintained by the state (a pupil is a lycéen). In England, early 19c., lyceum was the name taken by a number of literary societies (based on a similar use in late 18c. French); in U.S., after c. 1820, it was taken by institutes that sponsored popular lectures in science and literature, and their halls. Related: Lyceal
Lycia: ancient name of a mountainous district of southwestern Asia Minor, inhabited in ancient times by a distinct people, influential in Greece. The name is perhaps related to Greek lykos "wolf." Related: Lycian.
Lycoperdon: fungus genus established 1700 (Tournefort) for the "puffball" mushrooms, from Latinized form of Greek lykos "wolf" (see wolf (n.)) + perdesthai "to break wind," from PIE imitative root *perd-.
Lycra: elastic polyurethane fiber, 1955, proprietary name (registered by E.I. DuPont de Nemours and Company, Wilmington, Delaware, U.S.) of an elastic polyurethane fiber.
Lycurgus: Latinized form of Greek Lykourgos, name of the traditional law-giver of Sparta and author of its extraordinary constitution.
Lydia: ancient country of Asia Minor bordering the Aegean. It was an empire under Croesus, famous for his wealth. The name is from a supposed ancestor Ludos. The people also figure, as Ludim, in the Old Testament (Genesis x.13), which seems to have sometimes confused them with the Libyans. Related: Lydian, attested from 1540s as a noun, 1580s as an adjective, and 1570s as a musical mode.
lye (n.): Old English læg, leag "lye, water impregnated with alkaline salt absorbed from the ashes of wood by leaching," from Proto-Germanic *laugo (source also of Middle Dutch loghe, Dutch loog, Old High German louga, German Lauge "lye"), from PIE root *leue- "to wash."

The substance formerly was used in place of soap, hence Old High German luhhen "to wash," Old Norse laug "hot bath, hot spring," Danish lørdag, Swedish lördag "Saturday," literally "washing-day," "the day appropriated by the Scandinavians to that exercise" [Century Dictionary]. Chamber-lye in early Modern English was the name for urine used as a detergent.
lying (n.2): "untruthfulness, falsehood," c. 1300, "the telling of lies," verbal noun from lie (v.1) "to tell an untruth."
lying (n.1): "reclining," early 13c., verbal noun from lie (v.2) "to recline." Lying-in "a being in childbed" is attested from mid-15c.
lying (adj.1): "being prostrate," late Old English, present-participle adjective from lie (v.2) "to recline."
lying (adj.2): "untruthful," early 13c., present-participle adjective from lie (v.1) "to tell an untruth." Related: Lyingly.
lymph (n.): in physiology, "colorless fluid found in animal bodies," 1725, from French lymphe (16c.), from Latin lympha "water, clear water, a goddess of water," variant of lumpæ "waters," altered by influence of Greek nymphe "goddess of a spring, nymph."

The same word was used earlier in English in the classical sense "pure water, water" (1620s) and with reference to colorless fluids in plants (1670s). Also see lymphatic. Lymph node is attested from 1892.
lymphadenopathy (n.): 1899, from lymphadeno- "pertaining to a lymph gland" (from lymph + Greek adenos, genitive of aden "gland") + -pathy. Lymphadenoma is from 1873.
lymphatic (adj.): 1640s, from Modern Latin lymphaticus "pertaining to the lymph," from Latin lympha (see lymph). The English word also sometimes is used in what was the primary sense of lymphaticus in classical Latin, "mad, frenzied." OED reports this meaning "difficult to account for," but perhaps due to association of lympha with nymphe; compare Greek nymphian "to be frenzy-stricken." Also sometimes in reference to the appearance or temperament of one thought to suffer from excess of lymph, "dull, sluggish, slow in thought or action, with flabby muscles and pale skin" (1834).