pulmo

Latin pulmo (genitive pulmonis) meant lung. It derived from an older form, likely connected to the Proto-Indo-European root *pleu-, meaning to float or flow. The connection was physical: lungs float in water because they are full of air. Butchers knew this. The lungs were the one organ that would not sink when tossed into a basin.

Galen dissected animal lungs extensively in the second century CE and described pulmonary circulation in terms that were partly right and mostly influential. He believed the lungs processed pneuma -- vital spirit drawn from the air. It was Ibn al-Nafis, a Syrian physician working in Cairo around 1242, who first correctly described pulmonary circulation: blood flows from the right side of the heart to the lungs and back to the left side. Europe did not learn of his work for centuries.

The adjective pulmonarius appeared in medieval medical Latin. English borrowed pulmonary in the 1650s, around the time that Marcello Malpighi in Bologna discovered capillaries in frog lungs in 1661, finally proving how blood moved through the pulmonary system at the microscopic level. The word arrived in English just as the organ was finally understood.

The Greek cousin of pulmo is pneumōn, also meaning lung, which gave English pneumonia and pneumatic. The relationship between pulmo and the English word pumpkin is real but distant: Greek pepōn (large melon) passed through Latin and French, influenced by the pulp-like softness that pulmo also named. Both words remember something spongy and air-filled.