Meaning
The kanji 肺 means lung — the pair of vital respiratory organs located inside the chest cavity that are responsible for breathing. In Japanese, 肺 is used in medical, scientific, and formal contexts when discussing the lungs as a biological organ or when describing respiratory health and disease.
This kanji is built from two distinct components. The left side is 月 (にくづき, nikuzuki), which is the body or flesh radical — a modified form of 肉 (meat/flesh) that appears in many kanji related to human anatomy, such as 胃 (stomach), 腸 (intestine), and 胸 (chest). Whenever you see this radical on the left side of a kanji, it is a reliable signal that the character relates to a body part or internal organ. The right side is 市 (city/market), which functions primarily as a phonetic component providing the reading ハイ, derived from the original Chinese pronunciation of the character.
The kanji has 9 strokes and is classified as a Jōyō kanji introduced at the secondary school level in Japan. It is listed at JLPT N1 — the highest and most advanced level — reflecting its specialized use in medical, academic, and formal written Japanese. While you may not hear 肺 in casual daily conversation, it is essential vocabulary for anyone working in healthcare, reading Japanese news, or studying at an advanced level.
In traditional East Asian medicine, the lungs (肺) were counted among the five vital organs (五臓, gozō), alongside the heart, liver, spleen, and kidneys. They were associated with the autumn season, the color white, and the emotion of grief or sadness — giving this single kanji a surprisingly rich cultural and philosophical dimension beyond its anatomical meaning.
Readings
On'yomi (音読み) — Chinese-derived readings
The kanji 肺 has one primary on'yomi reading:
ハイ (HAI) — This reading is derived from ancient Chinese and is used in virtually all compound words containing this kanji. It appears consistently in medical terminology, scientific writing, and formal contexts. Because 肺 was borrowed directly from Chinese medical texts, all of its vocabulary is built on this single on'yomi reading.
- 肺炎 (haien) — pneumonia; literally "lung inflammation," one of the most common and important medical terms using this kanji
- 肺活量 (haikatsuuryou) — vital capacity; the maximum amount of air the lungs can hold, used in fitness and medical testing
- 肺臓 (haizou) — the lungs; a more formal anatomical term often found in medical textbooks
- 肺癌 (haigan) — lung cancer; frequently encountered in health journalism and medical reports
Kun'yomi (訓読み) — Native Japanese readings
The kanji 肺 does not have any standard kun'yomi reading. This is common for anatomical and medical kanji in Japanese that were adopted wholesale from classical Chinese medical texts. Before the widespread use of kanji, ancient Japanese described the lungs using native phrases, but once the Chinese character 肺 was introduced, it replaced those expressions in formal and written contexts. As a result, you will only ever encounter 肺 in on'yomi-based compound words. This makes it slightly easier to learn — there is only one reading to remember.
Common Words & Compounds
Because 肺 is a medical and anatomical term, its compound words cluster around respiratory health, lung diseases, and medical procedures. Mastering these compounds is particularly valuable for reading Japanese news, medical documents, or health-related content.
Medical Conditions and Diseases:
- 肺炎 (haien) — pneumonia; one of the most frequently used compounds, essential N1 vocabulary
- 肺癌 (haigan) — lung cancer; a major public health topic in Japan and globally
- 肺結核 (haikekaku) — pulmonary tuberculosis; historically significant disease still referenced in medical contexts
- 肺水腫 (haisuishu) — pulmonary edema; fluid accumulation in the lungs
- 肺病 (haibyou) — lung disease; a general term for pulmonary illness
- 肺塞栓 (haisokusen) — pulmonary embolism; blockage of a pulmonary artery
Anatomy and Physiology:
- 肺臓 (haizou) — the lungs; formal anatomical designation used in textbooks
- 肺活量 (haikatsuuryou) — vital capacity; the total volume of air the lungs can hold
- 肺胞 (haihou) — pulmonary alveolus; the tiny air sacs where gas exchange occurs
- 肺動脈 (haidoumyaku) — pulmonary artery; carries deoxygenated blood from the heart to the lungs
- 肺静脈 (haijōmyaku) — pulmonary vein; carries oxygenated blood from lungs to the heart
- 肺機能 (haikinou) — lung function; assessed in respiratory health evaluations
Directional and General Terms:
- 両肺 (ryouhai) — both lungs
- 右肺 (uhai) — right lung
- 左肺 (sahai) — left lung
Example Sentences
肺は呼吸に欠かせない臓器です。
Hai wa kokyuu ni kakasenai zouki desu.
The lungs are an indispensable organ for breathing.
かれは肺炎にかかって、一週間入院した。
Kare wa haien ni kakatte, isshuukan nyuuin shita.
He came down with pneumonia and was hospitalized for a week.
喫煙は肺癌の主な原因のひとつだ。
Kitsuen wa haigan no omona gen'in no hitotsu da.
Smoking is one of the main causes of lung cancer.
医者は肺のレントゲンを撮るように言った。
Isha wa hai no rentogen wo toru you ni itta.
The doctor told me to get an X-ray of my lungs.
水泳は肺活量を増やすのに効果的だ。
Suiei wa haikatsuuryou wo fuyasu no ni koukateki da.
Swimming is effective for increasing lung capacity.
彼女は両肺に影があると診断された。
Kanojo wa ryouhai ni kage ga aru to shindan sareta.
She was diagnosed as having shadows on both lungs.
肺は酸素を血液に取り込む働きをしている。
Hai wa sanso wo ketsueki ni torikomu hataraki wo shite iru.
The lungs function to absorb oxygen into the blood.
禁煙すれば肺の機能が徐々に回復する。
Kin'en sureba hai no kinou ga jojo ni kaifuku suru.
If you quit smoking, lung function will gradually recover.
新型肺炎の感染者が急増している。
Shingata haien no kansensha ga kyuuzou shite iru.
The number of people infected with the new strain of pneumonia is rapidly increasing.
肺の検査を定期的に受けることが大切です。
Hai no kensa wo teikiteki ni ukeru koto ga taisetsu desu.
It is important to have regular lung check-ups.
Memory Tip
To remember the kanji 肺, look closely at its two building blocks. The left side 月 (nikuzuki) is the body and flesh radical — your reliable signal that this kanji is about an internal organ. The right side 市 looks like a bustling city market. Picture your lungs as the body's most active marketplace: oxygen arrives like fresh goods being delivered, and carbon dioxide departs like waste being hauled away — a constant, rhythmic exchange that never stops, not even while you sleep. The lungs are the body's (月) non-stop trading market (市), and that vivid image of endless busy exchange will lock the shape and meaning of 肺 into your memory. Every breath you take is a transaction.