Lung
Old English lungen, of Germanic origin; related to Dutch long and German Lunge, from an Indo-European root shared by light2; compare with lights.
wiktionary
From Middle English lunge, longe, from Old English lungen, from Proto-Germanic *lunganjō, an enlargement of *lungô(“the light organ, lung”), from Proto-Indo-European *lengʷʰ-(“not heavy, agile, nimble”); compare *h₁lengʷʰ-, whence ultimately also light. Cognate with West Frisian long, Dutch long, German Lunge, Danish lunge, Norwegian lunge, Swedish lunga, Icelandic lunga, and also Russian лёгкое(ljóxkoje)(lung), Ancient Greek ἐλαφρός(elaphrós, “light in weight”) and perhaps Albanian lungë(“blister, bulge”). Compare Latin levis and Old English lēoht (Modern English light). See also lights(“lungs”). Superseded non-native Middle English pomoun(“lung”), borrowed from Old French poumon, pomon(“lung”).
etymonline
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.
