Several parts combine into one character.

肺 is a phonetic-semantic compound: 月 (the "flesh" radical for body parts) + 巿 (fú, originally a depiction of branching, drooping plant tendrils — providing both the sound and a visual hint of branching anatomy). Critical visual caution: the right component 巿 looks almost identical to 市 (shì, "market") but differs by a single feature — in 巿, a vertical stroke passes straight through the top, whereas 市 has a separate dot above. Confusing the two is one of the most common kanji-recognition errors for learners.

Korean reading "pye." 肺活量 (pyehwallyang, lung capacity / vital capacity), 肺癌 (pyeam, lung cancer), 肺炎 (pyeryeom, pneumonia), 肺結核 (pyegyeolhaek, pulmonary tuberculosis), 心肺 (simpye, "heart-lung" = cardiopulmonary, used in 심폐소생술 cardiopulmonary resuscitation). 폐 saturates Korean medical terminology.

Mandarin fèi, 4th tone. 肺 (fèi, lung), 肺炎 (fèiyán, pneumonia — became globally familiar through the COVID-era term 新型冠状病毒肺炎 "novel coronavirus pneumonia"), 肺癌 (fèi'ái, lung cancer), 心肺 (xīnfèi, cardiopulmonary), 肺活量 (fèihuóliàng, lung capacity). The vocabulary parallels Korean almost exactly.

Japanese on-reading ハイ (hai) — 肺 (hai, lung), 肺活量 (haikatsuryō, lung capacity — measured in fitness tests during Japanese school physical education), 肺炎 (haien, pneumonia), 心肺 (shinpai — note this homophone with 心配 shinpai meaning "worry"; context disambiguates). 肺 has essentially no kun-reading in modern Japanese; the on-reading ハイ covers everyday medical and anatomical use.

Memory aid: flesh (月) plus 巿 (drooping branching tendrils) — the branching internal organ that fills with air. Distinguish 巿 from 市 (market) by checking the top stroke.