expression, ichidan verb
sleep together (man and woman); press bodies together (for warmth)
Euphemistic expression for sexual intimacy, or literally pressing skin together for warmth. Context determines the meaning.
寒い夜は肌を合わせて暖を取った。
On cold nights, we pressed our bodies together to keep warm.
二人は肌を合わせる関
The two of them became physically intimate.