Coup de grâce
A coup de grâce (/ˌkuː də ˈɡrɑːs/; French: [ku də ɡʁɑs] ⓘ lit. 'blow of mercy') is an act of mercy killing in which a person or animal is struck with a melee weapon or shot with a projectile to end their suffering from mortal wounds with or without their consent. Its meaning has extended to refer to the final event that causes a figurative death.
Today, a coup de grâce for incapacitated soldiers would be a war crime: the laws of war mandate caring for the incapacitated and prohibit mercy killing.