What's the meaning of the phrase 'Sleep with'?
Euphemism for 'have sexual intercourse with'.
What's the origin of the phrase 'Sleep with'?
'Sleep with' is a classic euphemism in that it efficiently conceals the true meaning of what is being spoken about to everyone apart from those who already know its meaning. I'm not able to locate the origin of the expression as there are few examples of it in print other than those that are quite recent. I suspect that the phrase wasn't used before the 20th century.
What we do know is that, when an amorous couple decide to 'sleep together', sleep is the last thing on their minds.