肺

The word refers specifically to the biological organ used for breathing. In Japanese, it is used primarily in medical, biological, or health-related contexts. It is a neutral, technical term and does not carry emotional or social connotations.

In daily conversation, it frequently appears in compound nouns related to health and fitness, such as 肺活量 (lung capacity), which is a common metric in sports and health check-ups. Unlike some other organs, "肺" is rarely used metaphorically in Japanese; it almost always refers to the physical organ.

When discussing health issues, it is often paired with specific diseases (e.g., 肺がん - lung cancer) or symptoms (e.g., 肺に負担がかかる - putting a strain on the lungs).