coup de grâce

An action or event that brings a swift end to suffering or a worsening situation. The phrase is French for "blow of mercy." The samurai delivered a merciful coup de grâce to his mortally wounded enemy. The large class action lawsuit was the coup de grâce that caused the failing company to finally go out of business.

Finishing stroke. The phrase is French for “blow of mercy,” a death blow administered to end a wounded person’s suffering. It probably originated in dueling or other sword fighting and had been adopted into English by about 1700 and was already being used figuratively for the finishing stroke for any kind of enterprise. For example, “He carefully placed the figures of bride and groom on top of the cake, the coup de grâce for an artistic creation.”