Several parts combine into one character.

The traditional 寢 is a triple-component compound ideograph: 宀 (the "roof / house" radical) over 爿 (a wooden plank or board, used to depict a bed laid sideways) and 帚 (a broom). The composite picture is domestic and intimate: a swept-clean room, a bed, the act of lying down — literally "to lie down on a bed in a swept house" = to sleep. Few characters preserve such a complete bedtime tableau. Japan and Mainland China both simplified to 寝, reducing the broom component while preserving the roof and bed-plank structure. Korea retains the traditional 寢.

Korean reading "chim." 寢室 (chimsil, bedroom), 寢具 (chimgu, bedding), 寢臺 (chimdae, bed — Sino-Korean for what spoken Korean calls 침대), 就寢 (chwichim, "to enter sleep" = bedtime — formal), 不寢番 (bulchimbeon, "no-sleep watch" = the all-night sentry rotation in Korean military service, where conscripts take turns standing guard through the night). Korean (bed) is one of the few bedroom-related words borrowed wholesale from this character.

Mandarin qǐn, 3rd tone. 寝 (qǐn, sleep — formal), 寝室 (qǐnshì, dormitory room — used in Chinese university residence halls), 就寝 (jiùqǐn, to retire to bed), 寝车 (qǐnchē, sleeper car on a train). However, everyday Mandarin uses an entirely different verb for "to sleep": 睡觉 (shuìjiào). 寝 is reserved for formal, written, and compound contexts; spoken sentences like "I want to sleep" use 我要睡觉 (wǒ yào shuìjiào), never 我要寝.

Japanese on-reading シン (shin) — 寝室 (shinshitsu, bedroom), 就寝 (shūshin, going to bed — formal), 寝食 (shinshoku, "sleep and food" = daily life essentials). Kun-reading ねる (neru) is the everyday verb: 寝る (neru, to sleep / lie down), 寝かす (nekasu, to put to sleep / lay down), 寝坊 (nebō, oversleeping — extremely common excuse word). Critically, Japanese distinguishes 寝る (neru, the act of going to bed / lying down) from 眠る (nemuru, the state of unconscious sleep). 寝る は寝たけど眠れなかった ("I went to bed but couldn't sleep") demonstrates the split — 寝た is the bedding-down action, 眠れなかった is the failure of unconsciousness.

Memory aid: roof (宀) + bed (爿) + broom (帚) — a swept-clean room with a bed = sleep.