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to sleep, to go to bed
夜遅くまで起きていたので、早く寝ることにした。
I stayed up late, so I decided to go to bed early.
赤ちゃんはもう寝た。
The baby has already gone to sleep.
Often used to describe the action of going to sleep or lying down to rest.
to lie down (without necessarily sleeping)
疲れたので、ソファで少し寝る。
I'm tired, so I'll lie down on the sofa for a bit.
Can imply resting or taking a nap.
Avoid using '寝る' with objects. For example, '子供を寝る' is incorrect; use '子供を寝かせる' instead.
In formal contexts, use '寝ます' (the polite form) instead of '寝る'.
From Old Japanese 'neru', meaning 'to lie down' or 'to sleep'. The kanji '寝' (ne) is a phonetic component.
The verb '寝る' is intransitive and does not take a direct object. For transitive actions related to sleep, use '寝かせる' (to put to bed).