expression, ichidan verb
sleep together; lie with each other
Euphemistic expression for a man and woman having sexual relations; literally 'to layer skins'. Used in literary or indirect contexts.
二人は初めて肌を重ねた夜のことを、今でも鮮明に覚えている。
They still vividly remember the night they first slept together.
Compound of 肌 (はだ, 'skin') + を (object marker) + 重ねる (かさねる, 'to layer, pile up'). The literal image of 'layering skins' is a euphemism for sexual intimacy.