n 1 a  :  one of the usu. two compound saccular organs that constitute the basic respiratory organ of air-breathing vertebrates, that normally occupy the entire lateral parts of the thorax and consist essentially of an inverted tree of intricately branched bronchioles communicating with thin-walled terminal alveoli swathed in a network of delicate capillaries where the actual gaseous exchange of respiration takes place, and that in humans are somewhat flattened with a broad base resting against the diaphragm and have the right lung divided into three lobes and the left into two lobes  b  :  any of various respiratory organs of invertebrates  2  :  a mechanical device for regularly introducing fresh air into and withdrawing stale air from the lungs  :  RESPIRATOR - see IRON LUNG  lunged adj 
 
 
 
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