nighttime face powder; cosmetics applied before bed
Refers to powder or light makeup worn overnight, often to look presentable while sleeping or upon waking. Cross-referenced with 寝化粧, which is a related concept.
See also: 寝化粧
I hear that women in the past used to apply nighttime face powder before going to bed.
They say the inn's proprietress never skips her nighttime powder.
Compound of 寝 (ne, 'sleep') and 白粉 (oshiroi, 'white face powder'). The exact historical origin is uncertain, but it likely arose from the practice of wearing light powder to bed.