noun, noun or participle which takes 'suru'
sleeping together; sharing a bed
Literary or euphemistic term for two people sleeping together, often implying a sexual relationship. Rare in everyday conversation; more common words include 同衾 (どうきん) or simply 一緒に寝る.
二人は合衾の仲になった。
The two became intimate (literally, came to share a bed).
More common literary term for sleeping together; 合衾 is rarer and may carry a slightly more poetic or archaic nuance.
Composed of 合 (together) and 衾 (bedding, quilt). The exact historical derivation is uncertain; it is a Sino-Japanese compound used in literary contexts.