the Sword of Damocles hangs over someone
the Sword of Damocles hangs over someoneor
the Sword of Damocles hangs over someone's headLITERARY
If the Sword of Damocles hangs over someone or hangs over their head, they are in a situation in which something very bad could happen to them at any time. As a Grand Prix driver you have the Sword of Damocles hanging over your head at every moment. He lives with the illness, knowing that it is a Sword of Damocles, hanging over him. Note: This expression comes from a Greek legend. Dionysius, the ruler of Syracuse, was annoyed by Damocles, who kept flattering him and saying how much he admired him. Dionysius invited Damocles to a feast, and asked him to sit in his own seat. When Damocles looked up during the feast, he noticed a sword hanging by a single thread above his head, and so he could no longer enjoy the feast. The sword symbolized the dangers and fears that rulers have, in addition to all the privileges.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012