"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.

"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-.

"portable air tanks and apparatus for breathing underwater," 1950, from aqua- + lung. Developed 1943 by Jacques Cousteau and Emile Gagnan.

also lungfish, "type of freshwater fish having lung-like sacks that enable it to survive for a time out of water," 1883, from lung (n.) + fish (n.).

Proto-Indo-European root meaning "not heavy, having little weight."

It might form all or part of: alleviate; alleviation; alto-rilievo; carnival; elevate; elevation; elevator; leaven; legerdemain; leprechaun; Levant; levator; levee; lever; levity; levy (v.) "to raise or collect;" light (adj.1) "not heavy, having little weight;" lighter (n.1) "type of barge used in unloading;" lung; relevance; relevant; releve; relief; relieve.

It might also be the source of: Sanskrit laghuh "quick, small;" Greek elakhys "small," elaphros "light;" Latin levare "to raise," levis "light in weight, not heavy;" Old Church Slavonic liguku, Russian lëgkij, Polish lekki, Lithuanian lengvas "light in weight;" Old Irish lu "small," laigiu "smaller, worse;" Gothic leihts, Old English leoht "not heavy, light in weight."