Lights

google

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Middle English: use of light2 as a noun (so named because of their lightness). Compare with lung.

wiktionary

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lights

lights

etymonline

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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.