Sockdolager /(?)/

Sock·dol·a·ger

Sockdolager

n.
  1. That which finishes or ends a matter; a settler; a poser, as a heavy blow, a conclusive answer, and the like. [Slang, U.S.]
  2. A combination of two hooks which close upon each other, by means of a spring, as soon as the fish bites. (Angling) [U. S.]
  3. Something unusually large. [Slang, U. S.]