The word for today is…
coup de grâce (noun) – 1. A deathblow delivered to end the misery of a mortally wounded victim.
2. A finishing stroke or decisive event.
Source : The Free Dictionary
Etymology : Borrowed directly from French and first appearing in English at the end of the 17th century, coup de grâce (also sometimes styled without the circumflex as coup de grace) translates literally as “stroke of grace” or “blow of mercy,” and originally referred to a mercy killing, or to the act of putting to death a person or animal who was severely injured and unlikely to recover. (In some contexts the term is used to refer to the final act of executing a convicted criminal.) Later, coup de grâce had come to mean “an act or event that puts a definite end to something.” Other coup terms that have made the jump from French to English include coup de main, for a sudden, forceful attack, and coup d’état for a violent overthrow of a government usually by a small group.