Online Etymology Dictionary

Leghorn: breed of fowl, 1869, from Leghorn, city in Italy (modern Livorno, 16c.-17c. Legorno), from Latin Liburnus, from the native people name Liburni, which is of unknown signification.
legibility (n.): 1670s; see legible + -ity.
legible (adj.): late 14c., from Late Latin legibilis "that can be read," from Latin legere "to read" (see lecture (n.)). Related: Legibly.
legion (n.): c.1200, from Old French legion "Roman legion" (3,000 to 6,000 men, under Marius usually with attached cavalry), from Latin legionem (nominative legio) "body of soldiers," from legere "to choose, gather," also "to read" (see lecture (n.)).

Generalized sense of "a large number" is due to translations of allusive phrase in Mark v:9. American Legion, U.S. association of ex-servicemen, founded in 1919. Legion of Honor is French légion d'honneur, an order of distinction founded by Napoleon in 1802. Foreign Legion is French légion étrangère "body of foreign volunteers in a modern army," originally Polish, Belgian, etc. units in French army; they traditionally served in colonies or distant expeditions.
legionnaire (n.): 1818, from French légionnaire, from légion (see legion). Legionnaires' Disease, caused by Legionella pneumophilia, was named after the lethal outbreak of July 1976 at the American Legion convention in Philadelphia's Bellevue Stratford Hotel. Hence Legionella as the name of the bacterium that causes it.
legislate (v.): 1805, back-formation from legislation, etc. Related: Legislated; legislating.
legislation (n.): 1650s, from French législation, from Late Latin legislationem (nominative legislatio), properly two words, legis latio, "proposing (literally 'bearing') of a law;" see legislator.
legislative (adj.): 1640s; from legislator + -ive. Related: Legislatively.
legislator (n.): c.1600, from Latin legis lator "proposer of a law," from legis, genitive of lex "law" + lator "proposer," agent noun of latus "borne, brought, carried" (see oblate (n.)), used as past tense of ferre "to carry" (see infer). Fem. form legislatrix is from 1670s.
legislature (n.): 1670s; see legislator + -ure.
legit: colloquial shortening of legitimate, 1897, originally in theater, in reference to legitimate drama, that which has literary merit (Shakespeare, etc.).
legitimacy (n.): 1690s, of children; general use by 1836; see legitimate + -cy. Legitimateness an earlier word for it.
legitimate (adj.): mid-15c., "lawfully begotten," from Middle French legitimer and directly from Medieval Latin legitimatus, past participle of legitimare "make lawful, declare to be lawful," from Latin legitimus "lawful," originally "fixed by law, in line with the law," from lex (genitive legis) "law" (see legal). Transferred sense of "genuine, real" is attested from 1550s. Related: Legitimately.
legitimate (v.): 1590s, from Medieval Latin legitimatus, past participle of legitimare (see legitimate (adj.)). Related: Legitimated; legitimating.
legitimation (n.): mid-15c., from Middle French légitimation, from Medieval Latin legitimationem (nominative legitimatio), noun of action from past participle stem of legitimare (see legitimate (adj.)).
legitimism (n.): 1877, from French légitimisme; see legitimate (adj.) + -ism.
legitimist (n.): 1841, from French légitimiste, from légitime (see legitimate).
legitimize (v.): 1795, from Latin legitimus (see legitimate) + -ize. Earlier was legitimatize (1791). Related: Legitimized; legitimizing.
legless (adj.): 1590s, from leg (n.) + -less. Related: Leglessly; leglessness.
Lego: 1954, proprietary name (in use since 1934, according to the company), from Danish phrase leg godt "play well." The founder, Ole Kirk Christiansen, didn't realize until later that the word meant "I study" or "I put together" in Latin.
legume (n.): plant of the group of the pulse family, 1670s, from French légume (16c.), from Latin legumen "pulse, leguminous plant," of unknown origin. One suggestion ties it to Latin legere "to gather" (see lecture (n.)), because they can be scooped by the handful. Used in Middle English in the Latin form legumen (late 14c.).
leguminous (adj.): early 15c., from Latin legumen (see legume) + -ous.
lei (n.): 1843, from Hawaiian, "ornament worn about the neck or head."
Leica: 1925, proprietary name of cameras made by firm of Ernst & Leitz Gesellschaft, Wetzlar, Germany.
Leicester: Ligera ceaster (early 10c.) "Roman Town of the People Called Ligore," a tribal name, of unknown origin. For second element, see Chester.
Leila: fem. proper name, from Arabic Laylah, literally "dark as night," from laylah "night."
leio-: word-forming element meaning "smooth," from Greek leio-, comb. form of leios "smooth." E.g. leiotrichy "condition of having straight, lank hair" (1924).
leisure (n.): early 14c., leisir, "opportunity to do something" (as in phrase at (one's) leisure), also "time at one's disposal," from Old French leisir (Modern French loisir) "capacity; permission; leisure, spare time; free will; idleness, inactivity," noun use of infinitive leisir "be permitted," from Latin licere "be permitted" (see licence). The -u- appeared 16c., probably on analogy of words like pleasure. Phrase leisured class attested by 1836.
leisurely (adj.): c.1600, from leisure (n.) + -ly (1). As an adverb, with -ly (2), from late 15c. Related: Leisureliness.
leitmotif (n.): 1876, "a musical figure to which some definite meaning is attached," from German Leitmotiv, literally "lead motive," from leiten "to lead" (see lead (v.1)) + Motiv (see motive). A term associated with Wagnerian musical drama, though the thing itself is at least as old as Mozart. "The leitmotif must be characteristic of the person or thing it is intended to represent." ["Elson's Music Dictionary"]
lek (v.): to engage in courtship displays of certain animals, 1871, probably from Swedish leka "to play," cognate of English dialectal verb lake (see lark (v.)).
leman (n.): "sweetheart, paramour" (archaic), late 13c., from Middle English leofman (c.1200), from Old English leof "dear" (see lief) + man "human being, person" (see man (n.)). Originally of either gender, though deliberate archaic usage tends to limit it to women.
lemma (n.): 1560s, first in mathematics, from Greek lemma (plural lemmata) "something received or taken; an argument; something taken for granted," from root of lambanein "to take" (see analemma).
lemming (n.): small arctic rodent, c.1600, from Norwegian lemming, from Old Norse lomundr "lemming." Perhaps from Lapp luomek. Figurative sense (in reference to their mass migrations that sometimes end in plunges into the sea) is from 1958.
lemniscus (n.): 1811, from Late Latin lemniscus "a pendent ribbon." from Greek lemniskos "woolen ribbon," perhaps originally or literally "of Lemnos," island in the Aegean. Related: Lemniscate (1781).
lemon (n.1): type of citrus fruit, c.1400, lymon, from Old French limon "citrus fruit" (12c.), via Provençal or Italian from Arabic laimun, from Persian limu(n), generic terms for citrus fruits (cf. lime (n.2)); cognate with Sanskrit nimbu "the lime." Slang meaning "a Quaalude" is 1960s, from Lemmon, name of a pharmaceutical company that once manufactured the drug.
lemon (n.2): "worthless thing," 1909, American English slang; from lemon (n.1), perhaps via criminal slang sense of "a person who is a loser, a simpleton," which is perhaps from the notion of someone a sharper can "suck the juice out of." A pool hall hustle was called a lemon game (1908); while to hand someone a lemon was British slang (1906) for "to pass off a sub-standard article as a good one." Or it simply may be a metaphor for something which leaves a bad taste in one's mouth.
lemonade (n.): 1660s, from French limonade (17c.); see lemon (n.1) + -ade. Earlier English spelling was lemonado (c.1640) with false Spanish ending.
lemony (adj.): 1846, from lemon (n.1) + -y (2). In Australia/New Zealand slang, also "irritated, angry" (1941).
lemur (n.): nocturnal Madagascar mammal, 1795, coined by Linnaeus, from Latin lemures (plural) "spirits of the dead" in Roman mythology.
The oldest usage of "lemur" for a primate that we are aware of is in Linnaeus's catalog of the Museum of King Adolf Frederick of Sweden (Tattersall, 1982); .... In this work, he explained his use of the name "lemur" thus: "Lemures dixi hos, quod noctu imprimis obambulant, hominibus quodanmodo similes, & lento passu vagantur [I call them lemurs, because they go around mainly by night, in a certain way similar to humans, and roam with a slow pace]" [Dunkel, Alexander R., et al., "Giant rabbits, marmosets, and British comedies: etymology of lemur names, part 1," in "Lemur News," vol. 16, 2011-2012, p.65]
Lemuria (1864) was the name given by English zoologist P.L. Sclater (1829-1913) to a hypothetical ancient continent connecting Africa and Southeastern Asia (and including Madagascar), which was hypothesized to explain phenomena now accounted for by continental drift. Earlier it was the name of the Roman feast of the Lemures.
Lena: fem. proper name, originally a shortened form of Helena or Magdalena.
Lenape: 1728, native name for Delaware Indians, said to mean "original people."
lend (v.): late 14c., from Old English lænan "to lend," from læn "loan" (see loan). Cognate with Dutch lenen, Old High German lehanon, German lehnen, also verbs derived from nouns. Past tense form, with terminal -d, became the principal form in Middle English on analogy of bend, send, etc.
lender (n.): Old English laenere, agent noun from lænan (see lend (v.)).
length (n.): Old English lengðu "length," from Proto-Germanic *langitho, noun of quality from *langgaz (root of Old English lang; see long) + -itho, abstract noun suffix.

Cognate with Old Norse lengd, Old Frisian lengethe, Dutch lengte. Figurative sense of "the distance one goes, extremity to which something is carried" is from 1690s. Phrase at length "to full extent" is attested from c.1500.
lengthen (v.): late 14c., from length + -en (1). Related: Lengthened; lengthening. Earlier verb was simply length (c.1300).
lengthways: 1590s, from length + -way, with adverbial genitive -s.
lengthwise (adv.): 1570s, from length + wise (n.). As an adjective by 1871.
lengthy (adj.): 1759, American English, from length + -y (2). Until c.1840 always characterized in British English as an Americanism.
This word has been very common among us, both in writing and in the language of conversation; but it has been so much ridiculed by Americans as well as Englishmen, that in writing it is now generally avoided. Mr. Webster has admitted it into his dictionary; but as need hardly be remarked it is not in any of the English ones. It is applied by us, as Mr. Webster justly observes, chiefly to writings or discourses. Thus we say, a lengthy pamphlet, a lengthy sermon, &c. The English would say, a long or (in the more familiar style) a longish sermon. [John Pickering, "A Vocabulary, or Collection of Words and Phrases Which Have Been Supposed to be Peculiar to the United States of America," Boston, 1816]
Related: Lengthily; lengthiness.
lenience (n.): 1796, from lenient + -ence.