In careful or old-fashioned English, Morpheus is a way of talking about sleep. The usual phrase is in the arms of Morpheus, which means “asleep” — often deeply asleep, the kind that comes with dreams. It is literary. You will meet it in novels, poems, and slightly jokey writing that wants an old, bookish flavour. You would not say it at the breakfast table unless you were playing with words. The name belongs to the ancient Greek god of dreams. In the stories, he came into people’s sleep and took the shape of different people, so the dream felt real. Though actually, many students only know Morpheus as a character in the film The Matrix. That name was borrowed from this god. The film character is not what this English phrase is doing; here the word is a soft, old way to say someone has gone to sleep.