coup de grâce

noun2

1. •
   A final blow or shot given to kill a wounded person or animal.

   • After we had row'd, or rather driven about a League and a Half, as we reckon'd it, a raging Wave, Mountain-like, came rolling a-stern of us, and plainly bad us expect the Coup-de-Grace. — 1719
2. •
   (figurative) A remarkable finishing action.