also: ふしんばん
noun
sleepless vigil; night watch
Refers to staying awake all night to keep watch, often in a military, security, or traditional context. Can also imply general vigilance.
兵士たちは不寝番に立った。
The soldiers stood a sleepless vigil.
不寝番を命じられた。
I was ordered to keep night watch.
Compound of 不寝 (fushin/nezu, 'sleeplessness') and 番 (ban, 'watch'). The reading ねず is a native Japanese word for sleeplessness, while ふしん is a Sino-Japanese reading. The exact historical derivation is uncertain.