睡眠
shuìmián · HSK 5
sleep
😴 睡 = sleep + 眠 = slumber; both characters mean sleep, doubled for the noun
睡 (shuì) is the everyday verb to sleep; 眠 (mián) is a more literary sleep/slumber, sharing the 目 eye radical. Pairing them gives the formal noun for sleep, like saying slumber-sleep.
睡 — eye 目 + drooping 垂
睡 is a semantic compound: 目 (eye) signals the meaning, while 垂 (to droop, hang down) suggests eyelids falling. Together they depict drooping eyelids, i.e. dozing off. The original sense was nodding off while sitting; it later broadened to mean sleep in general.