1704, from L.
pulmonarius "of the lungs," from
pulmonem (nom.
pulmo, gen.
pulmonis) "lung," cognate with Gk.
pleumon "lung," O.C.S.
plusta, Lith.
plauciai "lungs," all from PIE
*pleu- "to flow, to float, to swim" (see
pluvial). The notion probably is from the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not. (cf. M.E.
lights "the lungs," lit. "the light (in weight) organs").