ダモクレスの剣つるぎ

also: ダモクレスのけん

Meanings

sword of Damocles

Refers to an ever-present danger or threat, especially one that hangs over someone in a position of power or good fortune. Used metaphorically in the same way as the English phrase.

核かく兵へい器きは人じん類るいにとってダモクレスの剣つるぎだ。
Nuclear weapons are a sword of Damocles hanging over humanity.
彼かれの成せい功こうはダモクレスの剣つるぎの上うえに成なり立たっている。
His success rests under the sword of Damocles.