Etymology
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lights (n.)
"the lungs," c. 1200, literally "the light (in weight) organs," from light (adj.1); also see lung. Obsolete now except in phrases like to knock (someone's) lights out.
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pulmonary (adj.)

"of or pertaining to the lungs; affecting the lungs; done by means of the lungs," 1704, from French pulmonaire and directly from Latin pulmonarius "of the lungs," from pulmo (genitive pulmonis) "lung(s)," cognate with Greek pleumon "lung," Old Church Slavonic plusta, Lithuanian plaučiai "lungs," all from PIE -*pl(e)umon- "lung(s)," literally "floater," suffixed form of root *pleu- "to flow."

The explanation behind the proposed PIE etymology is the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not. Compare Middle English lights "the lungs," literally "the light (in weight) organs." Also see pneumo-.

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lung (n.)

human or animal respiratory organ, c. 1300, from Old English lungen (plural), from Proto-Germanic *lunganjo- (source also of Old Norse lunge, Old Frisian lungen, Middle Dutch longhe, Dutch long, Old High German lungun, German lunge "lung"), literally "the light organ," from PIE root *legwh- "not heavy, having little weight" (source also of Russian lëgkij, Polish lekki "light;" Russian lëgkoje "lung").

So called perhaps because in a cook pot lungs of a slaughtered animal float, while the heart, liver, etc., do not. Compare Portuguese leve "lung," from Latin levis "light;" Irish scaman "lungs," from scaman "light;" Welsh ysgyfaint "lungs," from ysgafn "light." See also lights, pulmonary. Lung cancer is attested from 1882. Lung-power "strength of voice" is from 1900.

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lighthouse (n.)
tower exhibiting lights to warn mariners of rocks, shoals, etc., 1620s, from light (n.) + house (n.).
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dimmer (n.)

"one who or that which makes dim," 1822, agent noun from dim (v.). Of mechanisms for reducing the brightness of electric lights, from 1905.

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footlights (n.)
"row of lights placed in front of a stage" (formerly called floats), 1836, from foot (n.) of the stage + light (n.).
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brown-out (n.)
"partial blackout," 1942, based on blackout in the "dousing of lights as an air raid precaution" sense; from brown (adj.) as "not quite black."
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highlight (v.)

1861, "to give high lights to" (a painting, engraving, etc.), from highlight (n.). Figurative sense of "give prominence to, emphasize" is by 1944. Hairdressing sense is 1942. Related: Highlighted; highlighting.

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lighter (n.2)
"person who lights," 1550s, agent noun from light (v.2). From 1851 of devices or instruments to lighting gas-jets or candles (originally often a simple twist of paper rolled into a tapering tube); from 1895 of mechanical cigarette lighters.
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fluorescent (adj.)
1853 (Stokes), from fluor- (see fluoro-) + -escent. Also see fluorescence. The electric fluorescent lamp was invented by Edison in 1896, but such lights were rare in homes before improved bulbs became available in the mid-1930s.
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