'就寝' is a formal, written verb meaning 'to go to bed' or 'to retire for the night.' It combines 就 (jiù), which here conveys the sense of 'to assume a position or state,' and 寝 (qǐn), meaning 'sleep' or 'bed.' Together, they form an elegant, somewhat literary expression for the act of getting into bed to sleep — not merely lying down, but beginning the nighttime rest period. It is rarely used in casual speech and appears most often in official notices, school regulations, medical instructions, or formal writing.

The word carries a tone of discipline, routine, or authority: it implies adherence to a scheduled or appropriate time for sleep. You’ll commonly see it in contexts like boarding schools ('students must 就寝 by 10 p.m.'), hospital guidelines, or parental reminders to children. It’s not used for napping or falling asleep unintentionally — those require other terms like 睡觉 or 打盹. Its formality makes it unsuitable for texting friends or informal conversation.