noun
dead of night; all-night vigil
Literary or poetic term. Can refer to the deep, still hours of the night, or to the practice of staying awake all night in prayer at a shrine or temple. The religious sense is less common in modern everyday language.
夜籠りの静けさの中で、月明かりだけが庭を照らしていた。
In the stillness of the dead of night, only the moonlight illuminated the garden.
古い寺では、今でも年に一度、夜籠りの行事が行われている。
At the old temple, an all-night vigil is still held once a year.
Compound of 夜 (yo, 'night') and 籠り (komori, 'seclusion' or 'staying inside'), from the verb 籠る (komoru). The exact historical derivation is uncertain, but the word evokes the image of being shut in or enveloped by the night.