Lung/lʌŋ/ Definition 1 of 2Pro Tip 1/3Bodily Function Lung relates to breathing and oxygen exchange vital for life. Doctors check lung function to ensure healthy breathing. Pro Tip 2/3Health Context Lung is often used when discussing respiratory health and illnesses. He is recovering from a severe lung infection. Pro Tip 3/3Metaphorical Use Sometimes 'lung' describes things that function like a breathing organ. Forests are often called the lungs of the Earth.