Online Etymology Dictionary

locavore (n.): one who eats only locally grown or raised food, by 2001, from local + ending abstracted from carnivore, etc., ultimately from Latin vorare "to devour" (see voracity).
loch (n.): late 14c., from Gaelic loch "lake, narrow arm of the sea," cognate with Old Irish loch "body of water, lake," Breton lagen, Anglo-Irish lough, Latin lacus (see lake (n.1)). The Loch Ness monster is first attested 1933.
lochia (n.): "discharge from the uterus after childbirth," 1680s, Modern Latin, from Greek lokhia, neuter plural of lokhios "pertaining to childbirth," from lokhos "a lying in, childbirth," also, "an ambush," from PIE root *legh- "to lie, lay" (see lie (v.2)).
lock (n.1): "means of fastening," Old English loc "bolt, fastening; barrier, enclosure," from Proto-Germanic *lukan (source also of Old Norse lok "fastening, lock," Gothic usluks "opening," Old High German loh "dungeon," German Loch "opening, hole," Dutch luik "shutter, trapdoor"). "The great diversity of meaning in the Teut. words seems to indicate two or more independent but formally identical substantival formations from the root."

The Old English sense "barrier, enclosure" led to the specific meaning "barrier on a river" (c. 1300), and the more specific sense "gate and sluice system on a water channel used as a means of raising and lowering boats" (1570s). Wrestling sense is from c. 1600. Phrase under lock and key attested from early 14c.
lock (n.2): "tress of hair," Old English locc "lock of hair, curl," from Proto-Germanic *lukkoz (source also of Old Norse lokkr, Old Saxon, Old Frisian, Dutch lok, Old High German loc, German Locke "lock of hair"), from PIE *lugnos-, perhaps related to Greek lygos "pliant twig, withe," Lithuanian lugnas "flexible."
lock (v.): "to fasten with a lock," c. 1300, from Old English lucan "to lock, to close" (class II strong verb; past tense leac, past participle locen), from the same root as lock (n.1). Cognate with Old Frisian luka "to close," Old Saxon lukan, Old High German luhhan, Old Norse luka, Gothic galukan. Meaning "to embrace closely" is from 1610s. Related: Locked; locking. Slang lock horns "fight" is from 1839.
lock-jaw (n.): also lockjaw, 1786, earlier locked-jaw (1765), popular name for trismus, also applied to tetanus, from lock (v.) + jaw.
lock-step (n.): 1802, in military writing, for a very tight style of mass marching, from lock (n.) + step (n.).
Lock-step. A mode of marching by a body of men going one after another as closely as possible, in which the leg of each moves at the same time with and closely follows the corresponding leg of the person directly before him. [Thomas Wilhelm, "Military Dictionary and Gazetteer," Philadelphia, 1881]
Figurative use by 1836.
lock-up (n.): "detention cell for offenders," 1838, perhaps short for earlier lock-up house; from lock (v.) + up. Meaning "action of locking up" is from 1845. The verbal phrase lock up is recorded from early 15c.
lockable (adj.): 1832, from lock (v.) + -able. Related: Lockability.
lockdown (n.): also lock-down, from 1940s in various mechanical senses, from lock (v.) + down (adv.). Prison sense is by 1975, American English.
locker (n.): small chest that can be locked, late 14c., agent noun from Middle English lokken (see lock (v.)). Earlier "a mechanism for locking" (early 14c.).
locket (n.): mid-14c., "iron cross-bar of a window," from Old French loquet "door-handle, bolt, latch," diminutive of loc "lock, latch," from Frankish or some other Germanic source (compare Old Norse lok "fastening, lock;" see lock (n.1)). Meaning "ornamental case with hinged cover" (containing a lock of hair, miniature portrait, etc.) first recorded 1670s.
lockout (n.): also lock-out, "act of locking out workers," 1854, from lock (v.) + out.
locksmith (n.): early 13c., from lock (n.1) + smith.
loco (adj.): 1844, American English, from Spanish loco (adj.) "insane," of uncertain origin, perhaps from Arabic lauqa, fem. of 'alwaq "fool, crazy person." Loco-weed (1877) was name given to species of western U.S. plants that cause cattle and horse diseases that make them stagger and act strangely.
loco-: word-forming element meaning "from place to place," from comb. form of Latin locus (see locus).
loco-foco (n.): "self-igniting cigar or match," 1839 (but presumably older), American English, of unknown origin, perhaps from a misapprehension of the meaning of the first element of locomotive as "self-" + Spanish fuego "fire." During one heated political meeting in N.Y., the lights went out and the delegates used such matches to relight them, thence the name loco-foco entered U.S. political jargon (1837), usually applied to a radical faction of the Democratic Party, but by the Whigs applied to all Democrats.
locomote (v.): 1831, back-formation from locomotion.
locomotion (n.): 1640s, formed in English from Latin loco "from a place" (ablative of locus "place") + motionem (nominative motio) "motion, a moving."
locomotive (adj.): 1610s, "pertaining to movement," from French locomotif, from Latin loco "from a place" (ablative of locus "place;" see locus) + Late Latin motivus "moving" (see motive). The noun meaning "railroad engine" is from 1829, short for locomotive engine (1814).
locomotor (adj.): 1822, from Latin loco "from a place" (ablative of locus "place;" see locus) + motor.
locum tenens (n.): Medieval Latin, "one who holds the place (of another);" from locum (nominative locus; see locus) + tenens, present participle of tenere (see tenant).
locus (n.): (plural loci), 1715, "locality," from Latin locus "a place, spot, position," from Old Latin stlocus, literally "where something is placed," from PIE root *st(h)el- "to cause to stand, to place." Used by Latin writers for Greek topos. Mathematical sense by 1750.
locust (n.1): "grasshopper," early 14c., borrowed earlier in Old French form languste (c. 1200), from Latin locusta "locust, lobster" (see lobster).
In the Hebrew Bible there are nine different names for the insect or for particular species or varieties; in the English Bible they are rendered sometimes 'locust,' sometimes 'beetle,' 'grasshopper,' 'caterpillar,' 'palmerworm,' etc. The precise application of several names is unknown. [OED]
locust (n.2): North American tree, 1630s, originally "carob tree" (1610s), whose fruit supposedly resembled the insect (see locust (n.1)). Greek akris "locust" often was applied in the Levant to carob pods. Soon applied in English to other trees as well.
locution (n.): "style of speech," early 15c., from Latin locutionem (nominative locutio) "a speaking, speech, discourse; way of speaking," noun of action from past participle stem of loqui "to speak," from PIE root *tolk(w)- (source also of Old Irish ad-tluch- "to thank," to-tluch- "to ask;" Old Church Slavonic tloko "interpretation, explanation"). Related: Locutionary.
lode (n.): original Middle English spelling of load (n.), and custodian of most of the original meaning of "way, course, carrying." Differentiation in sense took place 16c. Mining sense of "vein of metal ore" is from c. 1600, from notion of miners "following" it through the rock.
loden (n.): "coarse woolen cloth," 1880, from German loden "thick woolen cloth."
lodestar (n.): late 14c. (late 13c. as a surname), an old name for the pole star (compare Old Norse leiðarstjarna) as the star that "leads the way" in navigation; from lode (n.) + star (n.). Figurative use from late 14c.
lodestone (n.): "magnetically polarized oxide of iron," 1510s, literally "way-stone," from lode + stone (n.). So called because it was used to make compass magnets to guide mariners. Figurative use from 1570s.
lodge (n.): mid-13c. in surnames and place names; late 13c. as "small building or hut," from Old French loge "arbor, covered walk; hut, cabin, grandstand at a tournament," from Frankish *laubja "shelter" (cognate with Old High German louba "porch, gallery," German Laube "bower, arbor"), from Proto-Germanic *laubja- "shelter," likely originally "shelter of foliage," or "roof made from bark," from root of leaf (n.).

"Hunter's cabin" sense is first recorded late 14c. Sense of "local branch of a society" is first recorded 1680s, from mid-14c. logge "workshop of masons." Also used of certain American Indian buildings, hence lodge-pole (1805). Feste of Logges (c. 1400) was a Middle English rendition of the Old Testament Jewish Feast of Tabernacles.
lodge (v.): c. 1200, loggen, "to encamp, set up camp;" c. 1300 "to put in a certain place," from Old French logier "lodge; find lodging for" (Modern French loger), from loge (see lodge (n.)). From late 14c. as "to dwell, live; to have temporary accomodations; to provide (someone) with sleeping quarters; to get lodgings." Sense of "to get a thing in the intended place, to make something stick" is from 1610s. Related: Lodged; lodging.
lodgement (n.): 1590s, from French logement (14c.) "accommodation, lodgings," from Old French logier (see lodge (v.)).
lodger (n.): early 14c., originally "tent-dweller," agent noun from lodge (v.). From c. 1200 as a surname. Meaning "one who lives in rented rooms" is from 1590s.
lodging (n.): early 14c., "encampment;" late 14c., "temporary accommodation; place of residence," verbal noun from lodge (v.). Related: Lodgings.
loess (n.): 1833 (in Lyell), "unstratified deposit of loam," coined 1823 by German mineralogist Karl Cäsar von Leonhard (1779-1862) from German Löss "yellowish-gray soil," from Swiss German lösch (adj.) "loose" (compare German los; see loose (adj.)). Related: Loessial.
loft (n.): "an upper chamber," c. 1300, from late Old English loft "the sky; the sphere of the air," from Old Norse lopt "air, sky," originally "upper story, loft, attic" (Scandinavian -pt- pronounced like -ft-), from Proto-Germanic *luftuz "air, sky" (source also of Old English lyft, Dutch lucht, Old High German luft, German Luft, Gothic luftus "air").

Sense development is from "loft, ceiling" to "sky, air." Buck suggests ultimate connection with Old High German louft "bark," louba "roof, attic," etc., with development from "bark" to "roof made of bark" to "ceiling," though this did not directly inform the meaning "air, sky." But Watkins says this is "probably a separate Germanic root." Meaning "gallery in a church" first attested c. 1500.
loft (v.): "to hit a ball high in the air," 1856, originally in golf, from loft (n.). Related: Lofted; lofting. An earlier sense was "to put a loft on" (a building), 1560s; also "to store (goods) in a loft" (1510s).
lofty (adj.): "exalted, of high rank," early 15c.; also "with a high purpose," from loft (n.) + -y (2). From early 14c. as a surname. Literal sense of "high" is attested from 1580s. Related: Loftily; loftiness.
log (n.1): unshaped large piece of tree, early 14c., of unknown origin. Old Norse had lag "felled tree" (from stem of liggja "to lie"), but on phonological grounds many etymologists deny that this is the root of English log. Instead, they suggest an independent formation meant to "express the notion of something massive by a word of appropriate sound." OED compares clog (n.) in its original Middle English sense "lump of wood." Log cabin (1770) in American English has been a figure of the honest pioneer since the 1840 presidential campaign of William Henry Harrison. Falling off a log as a type of something easy to do is from 1839.
log (v.2): "to enter into a log-book," 1823, from log (n.2). Meaning "to attain (a speed) as noted in a log" is recorded by 1883. Related: Logged; logging.
log (n.2): "record of observations, readings, etc.," 1842, sailor's shortening of log-book "daily record of a ship's speed, progress, etc." (1670s), from log (n.1). The book so called because a wooden float at the end of a line was cast out to measure a ship's speed. General sense by 1913.
log (v.1): "to fell a tree," 1717; earlier "to strip a tree" (1690s), from log (n.1). Related: Logged; logging.
log in (v.): 1963 in the computing sense, from log (v.2) + in (adv.).
loganberry (n.): 1893, American English, named for U.S. horticulturalist James H. Logan (1841-1928), who developed it by crossing a blackberry and a raspberry.
logarithm (n.): 1610s, Modern Latin logarithmus, coined by Scottish mathematician John Napier (1550-1617), literally "ratio-number," from Greek logos "proportion, ratio, word" (see logos) + arithmos "number" (see arithmetic).
logarithmic (adj.): 1690s, from logarithm + -ic. Related: Logarithmical (1630s).
logged (adj.): "reduced to the condition of a log" (which was old sailors' slang for an incapacitated wooden ship), thus "inert in the water," c. 1820, from log (n.1).
logger (n.1): "one who fells or cuts trees," by 1708, agent noun from log (v.1).