Online Etymology Dictionary

leniency (n.): 1780, from lenient + -cy.
lenient (adj.): 1650s, "relaxing, soothing," from Middle French lenient, from Latin lenientem (nominative leniens), present participle of lenire "to soften, alleviate, mitigate, allay, calm," from lenis "mild, gentle, calm," probably from PIE root *le- "to leave, yield, let go, slacken" (cf. Lithuanian lenas "quiet, tranquil, tame, slow," Old Church Slavonic lena "lazy," Latin lassus "faint, weary," Old English læt "sluggish, slow," lætan "to leave behind"). Sense of "mild, merciful" (of persons) first recorded 1787. In earlier use was lenitive, attested from early 15c. of medicines, 1610s of persons.
Lenin: pseudonym or alias chosen c.1902 (for publishing clandestine political works in exile) by Russian revolutionary Vladimir Il'ich Ulyanov (1870-1924). Related: Leninist (1917); Leninism (1918).
lenitive (adj.): early 15c., from Medieval Latin lenitivus, from Latin lenitus, past participle of lenire "to soften" (see lenient). As a noun, from early 15c.
lenity (n.): "softness," early 15c., from Middle French lénité or directly from Latin lenitatem (nominative lenitas), from lenis "soft, mild" (see lenient).
lens (n.): 1690s, "glass to regulate light rays," from Latin lens (genitive lentis) "lentil," on analogy of the double-convex shape. See lentil. Of the eye from 1719.
In the vernacular of the photographer, anyone crowding to the front of a group, staring into the lens, or otherwise attracting attention to himself is known as a "lens louse." ["American Photography," vol. 40, 1946; the term dates from 1915]
Lent (n.): late 14c., short for Lenten (n.) "forty days before Easter" (early 12c.), from Old English lencten "springtime, spring," the season, also "the fast of Lent," from West Germanic *langa-tinaz "long-days" (cf. Old Saxon lentin, Middle Dutch lenten, Old High German lengizin manoth), from *lanngaz (root of Old English lang "long;" see long (adj.)) + *tina-, a root meaning "day" (cf. Gothic sin-teins "daily"), cognate with Old Church Slavonic dini, Lithuanian diena, Latin dies "day" (see diurnal).

the compound probably refers to the increasing daylight. Cf. similar form evolution in Dutch lente (Middle Dutch lentin), German Lenz (Old High German lengizin) "spring." Church sense of "period between Ash Wednesday and Easter" is peculiar to English.
Lenten (adj.): late Old English, from Lent + -en (2). Elizabethan English had Lenten-faced "lean and dismal" (c.1600).
lenticular (adj.): early 15c., from Late Latin lenticularis, from lenticula "a small lentil," diminutive of lens "lentil" (see lentil). Related: Lenticularity.
lentil (n.): mid-13c., from Old French lentille "lentil," also "freckle," from Latin lenticula, diminutive of Latin lens (genitive lentis) "lentil," cognate with Greek lathyros, German linse, Old Church Slavonic lęšta.
lento: "slowly" (musical direction), 1724, from Italian lento "slow," from Latin lentus "flexible, pliant, slow, sluggish" (see lithe). Related: Lentissimo.
Leo: zodiac constellation, late Old English, from Latin leo "lion" (see lion). Meaning "person born under the sign of Leo" is from 1894. Leonid "meteor which appears to radiate from Leo" is from 1868. The annual shower peaks Nov. 14.
Leon: medieval kingdom in northwestern Spain, said to be from Latin legionis (septimae) "of the Seventh Legion," which was founded in Spain in 65 B.C.E.; the name probably then conformed to Spanish leon "lion." Related: Leonese.
Leonard: masc. proper name, from French Léonard, Old French Leonard, from German Leonhard, from Old High German *Lewenhart, literally "strong as a lion," from lewo (from Latin Leo, see lion) + hart "hard" (see hard (adj.)).
leonine (adj.): "lion-like," late 14c., from Old French leonin or directly from Latin leoninus "belonging to or resembling a lion," from leo (genitive leonis) "lion." Weekley thinks that Leonine verse (1650s), rhymed in the middle as well as the end of the line, probably is from the name of some medieval poet, perhaps Leo, Canon of St. Victor, Paris, 12c.
leopard (n.): late 13c., from Old French lebard, leupart (12c., Modern French léopard), from Late Latin leopardus, literally "lion-pard," from Greek leopardos, from leon "lion" + pardos "male panther," which generally is said to be connected to Sanskrit prdakuh "panther, tiger." The animal was thought in ancient times to be a hybrid of these two species.
Leopold: masc. proper name, from French Léopold, from Old High German Leutpald, Liutbald, literally "bold among the people," from leudi "people" + bald "bold."
leotard (n.): 1881, leotards, named for Jules Léotard (1830-1870), popular French trapeze artist, who performed in such a garment.
leper (n.): "one afflicted with leprosy," late 14c., from Late Latin lepra, from Greek lepra "leprosy," from fem. of lepros (adj.) "scaly," from leops "a scale," related to lepein "to peel," from lopos "a peel," from PIE root *lep- "to peel, scale" (see leaf). Originally the word for the disease itself (mid-13c.); because of the -er ending it came to mean "person with leprosy," so leprosy was coined 16c. from adjective leprous.
Lepidoptera (n.): 1773, "insects with four scaly wings," the biological classification that includes butterflies and moths, coined 1735 in Modern Latin by Swedish botanist Carolus Linnaeus (Karl von Linné, 1707-1778) from Greek lepido-, comb. form of lepis (genitive lepidos) "(fish) scale" (related to lepein "to peel;" see leper) + pteron "wing, feather" (see pterodactyl).
lepidopterist (n.): 1826, from Lepidoptera + -ist.
leprechaun (n.): c.1600, from Irish lupracan, metathesis from Old Irish luchorpan literally "a very small body," from lu "little" (from PIE *legwh- "having little weight;" see light (adj.)) + corpan, diminutive of corp "body," from Latin corpus "body" (see corporeal). Commonly spelled lubrican in 17c. English. Leithbragan is Irish folk etymology, from leith "half" + brog "brogue," because the spirit was "supposed to be always employed in making or mending a single shoe."
leprosy (n.): 1530s (earlier lepruse, mid-15c.), from leprous; see leper. First used in Coverdale Bible, where it renders Hebrew cara'ath, which apparently was a comprehensive term for skin diseases. Because of pejorative associations, the use of the word in medical context has been banned by the World Health Organization and replaced by Hansen's disease, named for Norwegian physician Armauer Hansen (1841-1912) who in 1871 discovered the bacillus that causes it.
leprous (adj.): early 13c., leprus, from Old French lepros (Modern French lépreux), from Late Latin leprosus, from Latin lepra "leprosy" (see leper).
lepton (n.): elementary particle of small mass, 1948, from Greek leptos "small, slight, slender, delicate" (from lepein "to peel," from PIE *lep-; see leper) + -on. Also the name of a small coin in ancient Greece, from neuter of leptos
lesbian (adj.): 1590s, "pertaining to the island of Lesbos," from Latin Lesbius, from Greek lesbios "of Lesbos," Greek island in northeastern Aegean Sea (the name originally may have meant "wooded"), home of Sappho, great lyric poet whose erotic and romantic verse embraced women as well as men, hence meaning "relating to homosexual relations between women" (1890; lesbianism in this sense is attested from 1870) and the noun, first recorded 1925. Before this, the principal figurative use (common in 17c.) was lesbian rule (c.1600) a mason's rule of lead, of a type used on Lesbos, which could be bent to fit the curves of a molding; hence, "pliant morality or judgment."
And this is the nature of the equitable, a correction of law where it is defective owing to its universality. ... For when the thing is indefinite the rule also is indefinite, like the leaden rule used in making the Lesbian moulding; the rule adapts itself to the shape of the stone and is not rigid, and so too the decree is adapted to the facts. [Aristotle, "Nicomachean Ethics"]
Cf. also tribadism.
lesbianism (n.): 1870, from lesbian + -ism.
lesbo: by 1940, colloquial shortening of lesbian.
lese-majesty (n.): "offense against sovereign authority, treason," 1530s (mid-15c. as an Anglo-French word), from French lèse-majesté, from Latin laesa majestos "violated majesty," from laesus, past participle of laedere "to hurt, injure, damage, offend, insult," of unknown origin.
lesion (n.): early 15c., from Middle French lesion, from Latin laesionem (nominative laesio) "injury," from past participle stem of laedere "to strike, hurt, damage," of unknown origin. Originally with reference to any sort of hurt, whether physical or not.
less: Old English læs (adv.), læssa (adj.), comparative of læs "small;" from Proto-Germanic *lais-izo "smaller" (cf. Old Saxon, Old Frisian les "less;" Middle Dutch lise "soft, gentle," German leise "soft"), from PIE root *leis- "small" (cf. Lithuanian liesas "thin"). Formerly also "younger," as a translation of Latin minor, a sense now obsolete except in James the Less. Used as a comparative of little, but not related to it. The noun is Old English læsse.
lessee (n.): "one to whom a lease is given," late 15c., from Anglo-French lesee, Old French lessé, past participle of lesser (Modern French laisser) "to let, leave" (see lease).
lessen (v.): "to become less," c.1300, from less + -en (1). Related: Lessened; lessening.
lesser (adj.): early 13c., a double comparative, from less + -er (2). Johnson calls it "a barbarous corruption of less, formed by the vulgar from the habit of terminating comparatives in -er." As an adverb from 1590s; now generally poetic or obsolete except in expression lesser-known (1813).
lesson (n.): early 13c., "a reading aloud from the Bible," also "something to be learned by a student," from Old French leçon, from Latin lectionem (nominative lectio) "a reading," noun of action from past participle stem of legere "to read" (see lecture (n.)). Transferred sense of "an occurrence from which something can be learned" is from 1580s.
lessor (n.): "one who grants a lease," late 14c., from Anglo-French lessor (late 13c.), from verb lesser (see lease).
lest (conj.): c.1200, contracted from Middle English phrase les te "less that," from Old English phrase þy læs þe "whereby less that," from þy, instrumental case of demonstrative article þæt "that" + læs (see less) + þe "the." The þy was dropped and the remaining two words contracted into leste.
let (v.): Old English lætan "to allow to remain; let go, leave, depart from; leave undone; to allow; bequeath," also "to rent" (class VII strong verb; past tense let, past participle læten), from Proto-Germanic *letan (cf. Old Saxon latan, Old Frisian leta, Dutch laten, German lassen, Gothic letan "to leave, let"), from PIE *le- "to let go, slacken" (cf. Latin lassus "faint, weary," Lithuanian leisti "to let, to let loose;" see lenient). If that derivation is correct, the primary sense would be "let go through weariness, neglect."

Of blood, from late Old English. To let (something) slip originally (1520s) was a reference to hounds on a leash; figurative use from 1540s. To let (someone) off "allow to go unpunished" is from 1814. To let on "reveal, divulge" is from 1725; to let up "cease, stop" is from 1787. Let alone "not to mention" is from 1812.
let (n.): "stoppage, obstruction" (obsolete unless in legal contracts), late 12c., from archaic verb letten "to hinder," from Old English lettan "hinder, delay," from Proto-Germanic *latjanan (cf. Old Saxon lettian "to hinder," Old Norse letja "to hold back," Old High German lezzen "to stop, check," Gothic latjan "to hinder, make late," Old English læt "sluggish, slow, late"); see late.
let up (n.): "cessation," 1837, from verbal phrase let up "cease, stop" (1787). In Old English the phrase meant "to put ashore."
letch (n.): "craving, longing," 1796, perhaps a back-formation from lecher, or from a figurative use of latch (v.) in a secondary sense of "grasp, grasp on to."
letdown (n.): also let-down, "disappointment," 1768, from let (v.) + down (adv.). The verbal phrase is from mid-12c. in a literal sense; figuratively by 1795.
lethal (adj.): 1580s, from Late Latin lethalis, alteration of Latin letalis "deadly, fatal," from letum "death," of uncertain origin. Form altered in Late Latin by association with lethe hydor "water of oblivion" in Hades in Greek mythology, from Greek lethe "forgetfulness."
lethality (n.): 1650s, from lethal + -ity.
lethargic (adj.): late 14c., litargik, from Latin lethargicus "affected with lethargy," from Greek lethargikos, from lethargos (see lethargy). Related: Lethargically.
lethargy (n.): late 14c., litarge, from Old French litargie or directly from Medieval Latin litargia, from Late Latin lethargia, from Greek lethargia "forgetfulness," from lethargos "forgetful," originally "inactive through forgetfulness," from lethe "forgetfulness" (see latent) + argos "idle" (see argon). The form with -th- is from 1590s in English.
Lethe: river of Hades (whose water when drunk caused forgetfulness of the past), from Greek lethe, literally "forgetfulness, oblivion," related to lethargos "forgetful," lathre "secretly, by stealth," lathrios "stealthy," lanthanein "to be hidden." Cognate with Latin latere "to be hidden" (see latent). Related: Lethean.
Letitia: fem. proper name, literally "gladness," from Latin laetitia, from laetus "glad," of unknown origin.
Lett: 1831, from German Lette, from Old High German liuti "people" (German Leute). The native name is Latvji (see Latvia). Related: Lettic; Lettish.
letter (n.1): c.1200, "graphic symbol, alphabetic sign, written character," from Old French letre (10c., Modern French lettre) "character, letter; missive, note," in plural, "literature, writing, learning," from Latin littera (also litera) "letter of the alphabet," of uncertain origin, perhaps via Etruscan from Greek diphthera "tablet," with change of d- to l- as in lachrymose. In this sense it replaced Old English bocstæf, literally "book staff" (cf. German Buchstabe "letter, character," from Old High German buohstab, from Proto-Germanic *bok-staba-m).

Latin littera also meant "a writing, document, record," and in plural litteræ "a letter, epistle," a sense first attested in English early 13c., replacing Old English ærendgewrit, literally "errand-writing." The Latin plural also meant "literature, books," and figuratively "learning, liberal education, schooling" (see letters). School letter in sports, attested by 1908, were said to have been first awarded by University of Chicago football coach Amos Alonzo Stagg. Expression to the letter "precisely" is from 1520s (earlier as after the letter). Letter-perfect is from 1845, originally in theater jargon, in reference to an actor knowing the lines exactly. Letter-press, in reference to matter printed from relief surfaces, is from 1840.