Several parts combine into one character.

腎 is a phono-semantic compound: 臤 (qián, "firm / hard" — itself a compound of 臣 "subject" + 又 "hand," giving the image of "firmly grasping") + 月 (flesh radical). 月 carries the meaning; 臤 lends both sound and a secondary connotation: "the firmly-set organ inside the body = kidney." East Asian traditional medicine treats 腎 as the seat of vital essence (精) and life force — a far broader concept than the Western anatomical kidney, encompassing reproductive vitality, deep stamina, and longevity.

Korean reading "shin." 腎臟 (shinjang, kidney — medical), 腎不全 (shin-bujeon, kidney failure), 副腎 (busin, adrenal gland — literally "secondary kidney"), 腎結石 (shin-gyeolseok, kidney stone). All medical Korean. Traditional Korean medicine (한의학) uses 腎 with the broader life-essence meaning, prescribing (bo-shin-tang, "kidney-tonifying soup") as a well-known summer-stamina dish.

Mandarin shèn, 4th tone. Simplified form 肾 — 肾 (shèn), 肾脏 (shènzàng, kidney), 肾炎 (shènyán, nephritis), 肾结石 (shènjiéshí, kidney stone). Identical medical vocabulary to Korean. Chinese traditional medicine retains the broader 腎 = "vital essence" reading especially in the phrase 补肾 (bǔ shèn, "to tonify the kidney") — a category of herbal supplements explicitly aimed at male sexual vitality and deep energy.

Japanese on-reading ジン (jin) — no kun reading in common use. 腎臓 (jinzō, kidney), 腎不全 (jinfuzen, kidney failure), 副腎 (fukujin, adrenal gland). Japanese medical vocabulary tracks the Korean and Chinese forms almost word-for-word — one of the most consistent CJK technical vocabularies, since modern medicine adopted these compounds together in the late 19th century.

Memory aid: 臤 ("firmly grasping") plus flesh (月) — the firm organ that holds the body's vital essence.