Pulmonary
mid 17th century: from Latin pulmonarius, from pulmo, pulmon- ‘lung’.
wiktionary
Borrowed from Latin pulmōnārius(“of the lungs”), from pulmō(“lung”) + -ārius, from Proto-Indo-European *pléu-mon-. Cognate with Greek πλεμόνι(plemóni), French poumon, Lithuanian plauciai, Polish płuco and Russian пла́вать(plávatʹ, “to swim”).
etymonline
pulmonary (adj.)
"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-.
