Online Etymology Dictionary

long-running (adj.): 1943, of theatrical productions, from long (adv.) + present participle of run (v.). Related: Longest-running.
long-suffering (adj.): also longsuffering, "bearing wrongs without retaliating," 1530s, from long (adj.) + suffering (n.). Old English had langmodig in this sense. From 1520s as a noun, "patience under offense."
long-tailed (adj.): c. 1500, from long (adj.) + tail (n.).
long-term (adj.): also longterm, 1876, originally in insurance underwriting, from long (adj.) + term (n.).
long-waisted (adj.): 1650s, from long (adj.) + waist (n.).
long-winded (adj.): also longwinded, 1580s, "given to lengthy speeches," from long (adj.) + adjective from wind (n.1) in the secondary Middle English sense "breath in speaking" (early 14c.). "Using much breath," hence "tedious from length."
longanimity (n.): "patience," mid-15c., from Late Latin longanimitas, from longanimus "long-suffering, patient," from longus "long, extended" (see long (adj.)) + animus "soul, spirit, mind" (see animus).
longbow (n.): also long-bow, the bow of war and chase in medieval Europe and the characteristic weapon of the English soldiery, only gradually superseded by firearms; late 14c., from long (adj.) + bow (n.1). Distinguished from the crossbow, but especially of bows five feet or longer.
longeron (n.): airplane part, 1912, from French longeron, from longer "to skirt, extend along," from allonger "to lengthen" (see lunge (n.)).
longevity (n.): 1610s, from Late Latin longaevitatem (nominative longaevitas) "great age, long life," from Latin longaevus "of great age, ancient, aged," from longus "long" (see long (adj.)) + aevum "lifetime, age" (see eon).
longhand (adj.): also long-hand, of handwriting in full (as opposed to shorthand), 1660s, from long (adj.) + hand (n.) "handwriting."
longhorn (adj.): also long-horn, in reference to a type of cattle, 1808, from long (adj.) + horn (n.).
longi-: word-forming element meaning "long," from Latin longi-, comb. form of longus "long" (see long (adj.)).
longing (n.): "yearning, eager desire, craving," Old English langung "longing, weariness, sadness, dejection," verbal noun from long (v.).
2. Specifically, in pathol., one of the peculiar and often whimsical desires experienced by pregnant women. [Century Dictionary, 1899]
longing (adj.): early 15c. (implied in longingly), present-participle adjective from long (v.).
longinquity (n.): "remoteness," 1540s, from Latin longinquitas "length, extent, duration," from longinquus "long, extensive, remote, distant," from longus "long; distant, remote" (see long (adj.)) + suffix -inquus.
longish (adj.): 1610s, from long (adj.) + -ish.
longitude (n.): late 14c., "length; height," also "astronomical or geographic longitude," a measure of the east-west distance of the dome of the sky or the surface of the earth, from Latin longitudo "length, long duration," from longus "long" (see long (adj.)). For explanation of the geographical sense, see latitude.
longitudinal (adj.): late 14c., from Medieval Latin longitudinalis, from Latin longitudo (see longitude).
longshanks (n.): "long-legged person," 1550s, originally in reference to Edward I of England (1239-1307); from long (adj.) + shank (n.).
longship (n.): also long-ship, Old English langscip "warship, man-of-war;" see long (adj.) + ship (n.). Translating Latin navis longa.
longshoreman (n.): "stevedore, one whose work is loading and unloading ships," 1811, from shortening of alongshore "existing or employed along a shore or coast" + man (n.).
longstanding (adj.): also long-standing, 1814, from earlier noun (c. 1600), from long (adj.) + standing (n.).
longtime (adj.): also long-time, 1580s, from long (adj.) + time (n.).
longways (adv.): "lengthwise," 1580s, from long (adj.) + way (n.) + adverbial genitive -s.
loo (n.1): "lavatory," 1940, but perhaps 1922 (based on a pun of Joyce's); perhaps [Dictionary of American Slang] from French lieux d'aisances "lavatory," literally "place of ease," picked up by British servicemen in France during World War I. Or possibly a pun on Waterloo, based on water closet.
loo (n.2): type of betting card game involving a hand of three cards, 1670s, short for lanterloo (1660s), from French lanturelu, originally (1620s) the refrain of a popular comic song; according to French sources the refrain expresses a mocking refusal or an evasive answer and was formed on the older word for a type of song chorus, turelure; apparently a jingling reduplication of loure "bagpipe" (which is perhaps from Latin lura "bag, purse").
From its primary signification -- a kind of bagpipe inflated from the mouth -- the word 'loure' came to mean an old dance, in slower rhythm than the gigue, generally in 6-4 time. As this was danced to the nasal tones of the 'loure,' the term 'loure' was gradually applied to any passage meant to be played in the style of the old bagpipe airs. ["Grove's Dictionary of Music and Musicians," London, 1906]
The refrain sometimes is met in English as turra-lurra. In the game, also the name of the pool or kitty of chips deposited by players before seeing their hands, or of the deposit made in it by a player.
looey (n.): 1916, American English, colloquial familiar form of lieutenant.
loof (n.): "palm of the hand," Scottish and Northern English, c. 1300, from Old Norse lofe "hand," which is said to be cognate with Gothic lofa, Russian lapa "paw," Lettish lepa "paw."
loofah (n.): 1879 (as lough, 1865), from Egyptian Arabic lufah, the name of the plant (Luffa ægyptiaca) with fibrous pods from which flesh-brushes are made.
loogie (n.): "nasal mucus," U.S. slang, by 1990.
look (v.): Old English locian "use the eyes for seeing, gaze, look, behold, spy," from West Germanic *lokjan (source also of Old Saxon lokon "see, look, spy," Middle Dutch loeken "to look," Old High German luogen, German dialectal lugen "to look out"), a word of unknown origin. Breton lagud "eye" has been suggested as a possible cognate.

In Old English, usually with on; the use of at began 14c. As a word to call attention, c. 1200. Meaning "seek, search out" is c. 1300; meaning "to have a certain appearance, express or manifest by looks" is from c. 1400. Of objects, "to face in a certain direction," late 14c. To look like "have the appearance of" is from mid-15c. Look after "take care of" is from late 14c., earlier "to seek" (c. 1300), "to look toward" (c. 1200). Look into "investigate" is from 1580s. To look forward "anticipate" is c. 1600; especially "anticipate with pleasure" from mid-19c. To look over "scrutinize" is from mid-15c.

Look up is from c. 1200 in literal sense "raise the eyes;" as "research in books or papers" from 1690s. To look up to "regard with respect and veneration" is from 1719. To look down upon in the figurative sense "regard as beneath one" is from 1711; to look down one's nose is from 1921. To not look back "make no pauses" is colloquial, first attested 1893. In look sharp (1711) sharp originally was an adverb, "sharply." To look around "search about, look round" is from 1883.
look (n.): late Old English, "act or action of looking," from look (v.). Meaning "a particular instance of looking, a glance," especially one which conveys a certain feeling is from early 14c. Meaning "appearance of a person, visual or facial expression" is from late 14c. Looks with the same sense as the singular is from 1560s. Expression if looks could kill ..., of one seething silently, is attested by 1827 (if looks could bite is attested from 1747). Fashion sense "totality of appearance" is from 1938.
look-alike (n.): "someone who closely resembles another," 1937, American English, from look (v.) + alike.
look-see (n.): "inspection," 1865, "Pidgin-like formation" [OED], first used in representations of English as spoken by Chinese, from look (v.) + see (v.).
lookdown (n.): type of sea fish, 1882, from look (v.) + down (adv.). So called from facial structure. Also known as moonfish, horsehead.
looker (n.): Old English locere "one engaged in looking," agent noun from look (v.). Meaning "one who watches over" is from c. 1300. Sense of "one who has a certain appearance" is late 15c.; slang meaning "attractive woman" attested from 1893 (good-looker is attested from 1866, both of women and horses). Looker-on "observer, spectator" is by 1590s; looker-in (1927) was an early word for "television viewer." In Middle English a lokere-oute was "one who divines by looking at entrails."
looking (n.): late 12c., "the action of looking," verbal noun from look (v.). From late 13c. as "look in the eyes, facial expression;" also "personal appearance, aspect." Looking-glass is from 1520s. The noun looking-in (1926) was an old expression for "television viewing."
lookit (interj.): noted by 1917 in schoolyard talk for look at.
lookout (n.): also look-out, "person who stands watch or acts as a scout," 1690s, from verbal phrase look out "be on the watch" (c. 1600), from look (v.) + out (adv.).
loom (n.): weaving machine, early 13c. shortening of Old English geloma "utensil, tool," from ge-, perfective prefix, + -loma, an element of unknown origin (compare Old English andloman (plural) "apparatus, article of furniture"). Originally "implement or tool of any kind" (as in heirloom); thus, "the penis" (c. 1400-1600). Specific meaning "a machine in which yarn or thread is woven into fabric" is from c. 1400.
loom (v.): 1540s, "to come into view largely and indistinctly," of uncertain origin. According to OED perhaps from a Scandinavian or Low German source (compare dialectal Swedish loma, East Frisian lomen "move slowly"), which is perhaps from the root of lame (adj.). Early used also of ships moving up and down. Figurative use from 1590s. Related: Loomed; looming.
loon (n.1): large diving bird (especially the Great Northern Diver), 1630s, apparently an alteration of loom in this sense, which is from a Scandinavian source (compare Norwegian lom, from Old Norse lomr "loon").
loon (n.2): mid-15c., lowen, louen "rascal, worthless person, boor," of uncertain origin, perhaps from Middle Dutch or Middle Low German; compare Dutch loen "stupid person" (16c.). The modern sense "crazy person" is by influence of loony.
loony (adj.): also loonie, looney, luny, "crazy; silly and eccentric," 1853, American English, short for lunatic, but also influenced by loon (n.2) and perhaps loon (n.1), the bird being noted for its wild cry and method of escaping from danger. As a noun by 1884, from the adjective.

Slang loony bin "insane asylum" is from 1919. Looney left in reference to holders of political views felt to be left-wing in the extreme is from 1977. Looney Tunes, Warner Bros. studios' animated cartoon series, dates from 1930.
loop (n.): late 14c., "a fold or doubling of cloth, rope, leather, cord, etc.," of uncertain origin. OED favors a Celtic origin (compare Gaelic lub "bend," Irish lubiam), which in English was perhaps influenced by or blended with Old Norse hlaup "a leap, run" (see leap (v.)). As a feature of a fingerprint, 1880. In reference to magnetic recording tape or film, first recorded 1931. Computer programming sense "sequence of instructions executed repeatedly" first attested 1947.
loop (v.): c. 1400, loupen, "to draw (a leash through a ring)," from loop (n.). Sense of "form into a loop or loops" (transitive) is from 1832; transitive meaning "form (something) into loops" is from 1856. Related: Looped (1934 in the slang sense "drunk"); looping. Loop the loop (1900) originally was in reference to roller-coasters at amusement parks.
"Loop-the-Loop" is the name of a new entertainment which goes further in the way of tempting Providence than anything yet invented. The "Loop" is an immense circle of track in the air. A car on a mimic railway shoots down a very steep incline, and is impelled around the inner side of this loop. ... The authorities at Coney Island are said to have prohibited "looping-the-loop" because women break their corset strings in their efforts to catch their breath as they sweep down the incline, and moreover, a young man is reported to have ruptured a blood vessel in his liver. ["Philadelphia Medical Journal," Aug. 10, 1901]
loophole (n.): also loop-hole, mid-15c., from hole (n.). + Middle English loupe "narrow window, slit-opening in a wall" for protection of archers while shooting, or for light and ventilation (c. 1300), which, along with Medieval Latin loupa, lobia probably is a specialized word from a continental Germanic source, such as Middle Dutch lupen "to watch, peer." Figurative sense of "outlet, means of escape" is from 1660s.
loopy (adj.): 1856, "full of loops," from loop (n.) + -y (2). Slang sense "crazy" is attested from 1923. The earlier figurative sense was "crafty, deceitful" (1824), popularized by Scott's novels.
loose (v.): c. 1200, lousen, "to set free, turn loose," also "undo, untie, unfasten," from loose (adj.). Of arrows from c. 1400. Related: Loosed; loosing.