1704, from L. pulmonarius
"of the lungs," from pulmonem
) "lung," cognate with Gk. pleumon
"lung," O.C.S. plusta,
"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").